Add no-render-return-value documentation

Author: yannickcr

README.md

@@ -83,6 +83,7 @@ The plugin has a [recommended configuration](#user-content-recommended-configura
 * [no-direct-mutation-state](docs/rules/no-direct-mutation-state.md): Prevent direct mutation of `this.state`
 * [no-is-mounted](docs/rules/no-is-mounted.md): Prevent usage of `isMounted`
 * [no-multi-comp](docs/rules/no-multi-comp.md): Prevent multiple component definition per file
+* [no-render-return-value](docs/rules/no-render-return-value.md): Prevent usage of the return value of `React.render`
 * [no-set-state](docs/rules/no-set-state.md): Prevent usage of `setState`
 * [no-string-refs](docs/rules/no-string-refs.md): Prevent using string references in `ref` attribute.
 * [no-unknown-property](docs/rules/no-unknown-property.md): Prevent usage of unknown DOM property (fixable)

docs/rules/no-render-return-value.md

@@ -0,0 +1,24 @@
+# Prevent usage of the return value of React.render (no-render-return-value)
+
+> `ReactDOM.render()` currently returns a reference to the root `ReactComponent` instance. However, using this return value is legacy and should be avoided because future versions of React may render components asynchronously in some cases. If you need a reference to the root `ReactComponent` instance, the preferred solution is to attach a [callback ref](http://facebook.github.io/react/docs/more-about-refs.html#the-ref-callback-attribute) to the root element.
+
+Source: [React Top-Level API documentation](http://facebook.github.io/react/docs/top-level-api.html#reactdom.render)
+
+## Rule Details
+
+This rule will warn you if you try to use the `ReactDOM.render()` return value.
+
+The following pattern is considered warning:
+
+```js
+const inst = ReactDOM.render(<App />, document.body);
+doSomethingWithInst(inst);
+```
+
+The following patterns are not considered warning:
+
+```js
+ReactDOM.render(<App ref={doSomethingWithInst} />, document.body);
+
+ReactDOM.render(<App />, document.body, doSomethingWithInst);
+```