modify markdown format of cluster_train_en.md and add link of demo/recommendation

doc/howto/usage/cluster/cluster_train_en.md

@@ -20,13 +20,13 @@ In this article, we explain how to run distributed Paddle training jobs on clust
 
 We refer to the directory where we put dependent libraries, config files, etc., as *workspace*.
 
-These ```train/test``` data should be prepared before launching cluster job. To  satisfy the requirement that train/test data are placed in different directory from workspace, PADDLE refers train/test data according to index file named as ```train.list/test.list``` which are used in model config file. So the train/test data also contains train.list/test.list two list file. All local training demo already provides scripts to help you create these two files,  and all nodes in cluster job will handle files with same logical code in normal condition.
+These `train/test` data should be prepared before launching cluster job. To  satisfy the requirement that train/test data are placed in different directory from workspace, PADDLE refers train/test data according to index file named as `train.list/test.list` which are used in model config file. So the train/test data also contains train.list/test.list two list file. All local training demo already provides scripts to help you create these two files,  and all nodes in cluster job will handle files with same logical code in normal condition.
 
-Generally, you can use same model file from local training for cluster training. What you should have in mind that, the ```batch_size``` set in ```setting``` function in model file means batch size in ```each``` node of cluster job instead of total batch size if synchronization SGD was used.
+Generally, you can use same model file from local training for cluster training. What you should have in mind that, the `batch_size` set in `setting` function in model file means batch size in `each` node of cluster job instead of total batch size if synchronization SGD was used.
 
-Following steps are based on demo/recommendation demo in demo directory.
+Following steps are based on [demo/recommendation](https://github.com/PaddlePaddle/Paddle/tree/develop/demo/recommendation) demo in demo directory.
 
-You just go through demo/recommendation tutorial doc until ```Train``` section, and at last you will get train/test data and model configuration file. Finaly, just use demo/recommendation as workspace for cluster training.
+You just go through demo/recommendation tutorial doc until `Train` section, and at last you will get train/test data and model configuration file. Finaly, just use demo/recommendation as workspace for cluster training.
 
 At last your workspace should look like as follow:
 ```
@@ -72,19 +72,19 @@ all files in data directory are refered by train.list/test.list which are refere
 
 The options below must be carefully set in cluster_train/conf.py
 
-```HOSTS```  all nodes hostname or ip that will run cluster job. You can also append user and ssh port with hostname, such as root@192.168.100.17:9090.
+`HOSTS`  all nodes hostname or ip that will run cluster job. You can also append user and ssh port with hostname, such as root@192.168.100.17:9090.
 
-```ROOT_DIR``` workspace ROOT directory for placing JOB workspace directory
+`ROOT_DIR` workspace ROOT directory for placing JOB workspace directory
 
-```PADDLE_NIC``` the NIC(Network Interface Card) interface name for cluster communication channel, such as eth0 for ethternet, ib0 for infiniband.
+`PADDLE_NIC` the NIC(Network Interface Card) interface name for cluster communication channel, such as eth0 for ethternet, ib0 for infiniband.
 
-```PADDLE_PORT``` port number for cluster commnunication channel
+`PADDLE_PORT` port number for cluster commnunication channel
 
-```PADDLE_PORTS_NUM``` the number of port used for cluster communication channle. if the number of cluster nodes is small(less than 5~6nodes), recommend you set it to larger, such as 2 ~ 8, for better network performance.
+`PADDLE_PORTS_NUM` the number of port used for cluster communication channle. if the number of cluster nodes is small(less than 5~6nodes), recommend you set it to larger, such as 2 ~ 8, for better network performance.
 
-```PADDLE_PORTS_NUM_FOR_SPARSE``` the number of port used for sparse updater cluster commnunication channel. if sparse remote update is used, set it like ```PADDLE_PORTS_NUM```
+`PADDLE_PORTS_NUM_FOR_SPARSE` the number of port used for sparse updater cluster commnunication channel. if sparse remote update is used, set it like `PADDLE_PORTS_NUM`
 
-```LD_LIBRARY_PATH``` set addtional LD_LIBRARY_PATH for cluster job. You can use it to set CUDA libraries path.
+`LD_LIBRARY_PATH` set addtional LD_LIBRARY_PATH for cluster job. You can use it to set CUDA libraries path.
 
 Default Configuration as follow:
 
@@ -118,15 +118,15 @@ LD_LIBRARY_PATH="/usr/local/cuda/lib64:/usr/lib64"
 ```
 
 ### Launching Cluster Job
-```paddle.py``` provides automatical scripts to start all PaddlePaddle cluster processes in different nodes. By default, all command line options can set as ```paddle.py``` command options and ```paddle.py``` will transparently and automatically set these options to PaddlePaddle lower level processes.
+`paddle.py` provides automatical scripts to start all PaddlePaddle cluster processes in different nodes. By default, all command line options can set as `paddle.py` command options and `paddle.py` will transparently and automatically set these options to PaddlePaddle lower level processes.
 
-```paddle.py```provides two distinguished command option for easy job launching.
+`paddle.py`provides two distinguished command option for easy job launching.
 
-```job_dispatch_package```  set it with local ```workspace```directory, it will be dispatched to all nodes set in conf.py. It could be helpful for frequent hacking workspace files, otherwise frequent mulit-nodes workspace deployment could make your crazy.
-```job_workspace```  set it with already deployed workspace directory, ```paddle.py``` will skip dispatch stage to directly launch cluster job with all nodes. It could help to reduce heavy
+`job_dispatch_package`  set it with local `workspace`directory, it will be dispatched to all nodes set in conf.py. It could be helpful for frequent hacking workspace files, otherwise frequent mulit-nodes workspace deployment could make your crazy.
+`job_workspace`  set it with already deployed workspace directory, `paddle.py` will skip dispatch stage to directly launch cluster job with all nodes. It could help to reduce heavy
 dispatch latency.
 
-```cluster_train/run.sh``` provides command line sample to run ```demo/recommendation``` cluster job, just modify ```job_dispatch_package``` and ```job_workspace``` with your defined directory, then:
+`cluster_train/run.sh` provides command line sample to run `demo/recommendation` cluster job, just modify `job_dispatch_package` and `job_workspace` with your defined directory, then:
 ```
 sh run.sh
 ```
@@ -134,7 +134,7 @@ sh run.sh
 The cluster Job will start in several seconds.
 
 ### Kill Cluster Job
-```paddle.py``` can capture ```Ctrl + C``` SIGINT signal to automatically kill all processes launched by it. So just stop ```paddle.py``` to kill cluster job. You should mannally kill job if program crashed.
+`paddle.py` can capture `Ctrl + C` SIGINT signal to automatically kill all processes launched by it. So just stop `paddle.py` to kill cluster job. You should mannally kill job if program crashed.
 
 ### Check Cluster Training Result
 Check log in $workspace/log for details, each node owns same log structure.
@@ -152,5 +152,5 @@ It provides stderr and stdout of pserver process. Check error log if training cr
 It provides stderr and stdout of trainer process. Check error log if training crashs.
 
 ### Check Model Output
-After one pass finished, model files will be writed in ```output``` directory in node 0.
-```nodefile``` in workspace indicates the node id of current cluster job.
+After one pass finished, model files will be writed in `output` directory in node 0.
+`nodefile` in workspace indicates the node id of current cluster job.