Add nvm node_mirror, npm_mirror usage in Readme.

README.md

@@ -74,6 +74,8 @@ NVM for Windows is a command line tool. Simply type `nvm` in the console for hel
 - `nvm use <version> [arch]`: Switch to use the specified version. Optionally specify 32/64bit architecture. `nvm use <arch>` will continue using the selected version, but switch to 32/64 bit mode based on the value supplied to `<arch>`.
 - `nvm root <path>`: Set the directory where nvm should store different versions of node.js. If `<path>` is not set, the current root will be displayed.
 - `nvm version`: Displays the current running version of NVM for Windows.
+- `nvm node_mirror <node_mirror_url>`: Set the node mirror.People in China can use *https://npm.taobao.org/mirrors/node/*
+- `nvm npm_mirror <npm_mirror_url>`: Set the npm mirror.People in China can use *https://npm.taobao.org/mirrors/npm/*
 
 ### Gotcha!