Merge pull request reactjs#269 from monkindey/yarn_link

correct `yarn link` usage

Author: bvaughn

content/docs/how-to-contribute.md

@@ -119,12 +119,15 @@ First, run `yarn build`. This will produce pre-built bundles in `build` folder,
 
 The easiest way to try your changes is to run `yarn build core,dom --type=UMD` and then open `fixtures/packaging/babel-standalone/dev.html`. This file already uses `react.development.js` from the `build` folder so it will pick up your changes.
 
-If you want to try your changes in your existing React project, you may copy `build/dist/react.development.js`, `build/dist/react-dom.development.js`, or any other build products into your app and use them instead of the stable version. If your project uses React from npm, you may delete `react` and `react-dom` in its dependencies and use `npm link` to point them to your local `build` folder:
+If you want to try your changes in your existing React project, you may copy `build/dist/react.development.js`, `build/dist/react-dom.development.js`, or any other build products into your app and use them instead of the stable version. If your project uses React from npm, you may delete `react` and `react-dom` in its dependencies and use `yarn link` to point them to your local `build` folder:
 
 ```sh
-cd your_project
-yarn link ~/path_to_your_react_clone/build/packages/react
-yarn link ~/path_to_your_react_clone/build/packages/react-dom
+cd ~/path_to_your_react_clone/build/packages/react
+yarn link
+cd ~/path_to_your_react_clone/build/packages/react-dom
+yarn link
+cd /path/to/your/project
+yarn link react react-dom
 ```
 
 Every time you run `yarn build` in the React folder, the updated versions will appear in your project's `node_modules`. You can then rebuild your project to try your changes.