docs(plugins): add IgnorePlugin documentation

Fixes #1014

Author: simon04

content/plugins/ignore-plugin.md

@@ -0,0 +1,24 @@
+---
+title: IgnorePlugin
+contributors:
+  - simon04
+---
+
+```js
+new webpack.IgnorePlugin(requestRegExp, [contextRegExp])
+```
+
+Don't generate modules for requests matching the provided RegExp.
+
+* `requestRegExp` A RegExp to test the request against.
+* `contextRegExp` (optional) A RegExp to test the context (directory) against.
+
+## Typical use-cases
+
+### Ignore moment locales
+
+As of [moment](https://momentjs.com/) 2.18, all locales are bundled together with the core library (see [this GitHub issue](https://github.com/moment/moment/issues/2373)). You can use the `IgnorePlugin` to stop any locale being bundled with moment:
+
+```js
+new webpack.IgnorePlugin(/^\.\/locale$/, /moment$/)
+```