Docs: fix demo_guide.

docs/demo_guide/README.md

@@ -28,8 +28,8 @@ Setup steps:
     ```
     rosbag play docs/demo_guide/demo.bag --loop
     # or 
-    bash docs/demo_guide/rosbag_helper.sh download #download rosbag
-    rosbag play docs/demo_guide/demo_1.5.np.bag --loop
+    sudo bash docs/demo_guide/rosbag_helper.sh download #download rosbag
+    rosbag play docs/demo_guide/demo_2.0.bag --loop
     ```
 
     The `--loop` option enables rosbag to keep playing the bag in a loop

docs/quickstart/apollo_1_0_quick_start.md

@@ -79,6 +79,7 @@ Before getting started, please make sure you have installed the Ubuntu Linux 14.
 ```
 git clone git@github.com:ApolloAuto/apollo.git
 cd apollo
+git checkout [release_branch_name]
 
 ```