Add customValidators option to prop-types documentation

Author: yannickcr

docs/rules/prop-types.md

@@ -8,7 +8,7 @@ It can warn other developers if they make a mistake while reusing the component
 
 The following patterns are considered warnings:
 
-```js
+```jsx
 var Hello = React.createClass({
   render: function() {
     return <div>Hello {this.props.name}</div>;
@@ -27,7 +27,7 @@ var Hello = React.createClass({
 
 The following patterns are not considered warnings:
 
-```js
+```jsx
 var Hello = React.createClass({
   render: function() {
     return <div>Hello World</div>;
@@ -58,12 +58,13 @@ This rule can take one argument to ignore some specific props during validation.
 
 ```
 ...
-"prop-types": [<enabled>, { ignore: <ignore> }]
+"prop-types": [<enabled>, { ignore: <ignore>, customValidators: <customValidator> }]
 ...
 ```
 
 * `enabled`: for enabling the rule. 0=off, 1=warn, 2=error. Defaults to 0.
 * `ignore`: optional array of props name to ignore during validation.
+* `customValidators`: optional array of validators used for propTypes validation.
 
 ### As for "exceptions"