chore(pr): add pr step instroduction

.github/CONTRIBUTING.md

@@ -14,6 +14,8 @@ Hi! I'm really excited that you are interested in contributing to Hippy. Before
 
 ## Pull Request Guidelines
 
+- Setting up your local environment to get started. You will need have [git](https://git-scm.com/) and [npm](https://docs.npmjs.com/downloading-and-installing-node-js-and-npm) installed locally, then run `npm install` to download all needed dependencies. These are detailed in the [Development Setup guide](https://github.com/Tencent/Hippy#getting-started). 
+
 - Checkout a topic branch from the relevant branch, e.g. `master`, and merge back against that branch.
 
 - Test cases have been added/updated/passed for the code you will submit.

README.md

@@ -23,9 +23,11 @@ Hippy is now applied in 27+ [Tencent](http://www.tencent.com/) apps such as Mobi
 
 ### Preparing environment
 
-Run `git clone https://github.com/Tencent/Hippy.git`
+Make sure you have [git](https://git-scm.com/) and [npm](https://docs.npmjs.com/downloading-and-installing-node-js-and-npm) installed locally.
 
-> Hippy repository applies [git-lfs](https://git-lfs.github.com/) to manage so,gz,otf files, make sure you have installed [git-lfs](https://git-lfs.github.com/) first.
+Run `git clone https://github.com/Tencent/Hippy.git` and `npm install` at project root directory.
+
+> The Hippy repository applies [git-lfs](https://git-lfs.github.com/) to manage so,gz,otf files, make sure you have installed [git-lfs](https://git-lfs.github.com/) first.
 
 For macOS developers:
 
@@ -147,6 +149,7 @@ Hippy
 ├── core                              # JS modules implemented by C++, binding to JS engine.
 ├── docker                            # Native release docker image and build scripts.
 ├── layout                            # Hippy layout engine.
+├── static                            # Global static resources stored directory.
 └── scripts                           # Project build script.
 ```
 

README.zh_CN.md

@@ -25,7 +25,9 @@ Hippy 是一个新生的跨端开发框架，目标是使开发者可以只写
 
 ### 准备环境
 
-运行 `git clone https://github.com/Tencent/Hippy.git`
+确保你本地已经安装 [git](https://git-scm.com/) 和 [npm](https://docs.npmjs.com/downloading-and-installing-node-js-and-npm) 。
+
+运行 `git clone https://github.com/Tencent/Hippy.git`，然后在项目根目录运行 `npm install`。
 
 > Hippy 仓库使用 [git-lfs](https://git-lfs.github.com/) 来管理 so,gz,otf 文件, 请确保你已经安装 [git-lfs](https://git-lfs.github.com/)。
 
@@ -146,6 +148,7 @@ Hippy
 ├── core                              # C++ 实现的 JS 模块，通过 Binding 方式运行在 JS 引擎中。
 ├── docker                            # 发布 Native 的 Docker 镜像和构建脚本
 ├── layout                            # Hippy 布局引擎。
+├── static                            # 全局静态资源存储目录。
 └── scripts                           # 项目编译脚本。
 ```