Provide instructions on virtualenv. (#258)

* Provide instructions on virtualenv.

* Clean up the detail a little bit.

README.cn.md

@@ -55,11 +55,13 @@ VisualDL 目前支持4种组件：
 </p>
 
 ## 快速尝试
+请使用下面的命令，来快速测试 VisualDL。
+
 ```
-# 安装
+# 安装，建議是在虛擬環境下。
 pip install --upgrade visualdl
 
-# 运行一个例子
+# 运行一个例子，vdl_scratch.py将创建测试日志
 vdl_scratch.py
 visualDL --logdir=scratch_log --port=8080
 

README.md

@@ -62,11 +62,13 @@ Histogram can be used to visualize parameter distribution and trends for any ten
 </p>
 
 ## Quick Start
+To give the VisualDL a quick test, please use the following commands.
+
 ```
-# install
+# Install the VisualDL. Preferably under a virtual environment.
 pip install --upgrade visualdl
 
-# run a demo
+# run a demo, vdl_scratch.py will create logs for testing.
 vdl_scratch.py
 visualDL --logdir=scratch_log --port=8080
 

docs/contribute_code_cn.md

@@ -27,6 +27,22 @@ VisualDL 目前使用[Git流分支模型](http://nvie.com/posts/a-successful-git
    ```bash
    git checkout -b my-cool-stuff
    ```
+1. Virtualenv
+
+   virtualenv是一个独立的Python虚拟环境。我们强烈建议您使用` virtualenv `来保持你的Python环境清洁。
+   要创建虚拟环境并激活它，请使用以下命令。
+
+   ```bash
+   pip install --upgrade virtualenv
+   virtualenv YOUR_VIRTUAL_EVN_FOLDER
+   source YOUR_VIRTUAL_EVN_FOLDER/bin/activate
+   ```
+
+   完成此工作后，可以通过操作来解除虚拟环境。
+   ```bash
+   deactivate
+   ```
+   要了解更多关于` virtualenv `，点击[这里]（https://virtualenv.pypa.io/en/stable/）
 
 1. commit
 

docs/contribute_code_en.md

@@ -29,6 +29,24 @@ VisualDL uses this [Git branching model](http://nvie.com/posts/a-successful-git-
    git checkout -b my-cool-stuff
    ```
 
+1. Virtualenv
+
+   VirtualEnv is an isolated virtual environment for Python. We highly recommend using `virtualenv` to keep your python environment clean.
+
+   To create a virtual environment and activate it, please use the following commands.
+   ```bash
+   pip install --upgrade virtualenv
+   virtualenv YOUR_VIRTUAL_EVN_FOLDER
+   source YOUR_VIRTUAL_EVN_FOLDER/bin/activate
+   ```
+
+   When you are done with the work, you can deactivate the virtual environment by doing.
+   ```bash
+   deactivate
+   ```
+
+   To learn more about `virtualenv`, click [here](https://virtualenv.pypa.io/en/stable/)
+
 1. Commit
 
    Before issuing your first `git commit` command, please install [`pre-commit`](http://pre-commit.com/) and other requirements by running the following commands: