Merge pull request airbnb#1302 from airbnb/mixins

Add guidance around not using mixins

Author: lencioni

react/README.md

@@ -28,7 +28,7 @@
 
 ## Class vs `React.createClass` vs stateless
 
-  - If you have internal state and/or refs, prefer `class extends React.Component` over `React.createClass` unless you have a very good reason to use mixins. eslint: [`react/prefer-es6-class`](https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/prefer-es6-class.md) [`react/prefer-stateless-function`](https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/prefer-stateless-function.md)
+  - If you have internal state and/or refs, prefer `class extends React.Component` over `React.createClass`. eslint: [`react/prefer-es6-class`](https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/prefer-es6-class.md) [`react/prefer-stateless-function`](https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/prefer-stateless-function.md)
 
     ```jsx
     // bad
@@ -69,6 +69,12 @@
     }
     ```
 
+## Mixins
+
+  - [Do not use mixins](https://facebook.github.io/react/blog/2016/07/13/mixins-considered-harmful.html).
+
+  > Why? Mixins introduce implicit dependencies, cause name clashes, and cause snowballing complexity. Most use cases for mixins can be accomplished in better ways via components, higher-order components, or utility modules.
+
 ## Naming
 
   - **Extensions**: Use `.jsx` extension for React components.