Add FallbackResource in documentation [Follow up]

So this is the follow up to my [last request](https://github.com/anandkunal/ToroPHP/pull/72). It just **adds** the encouraged use of `FallbackResource` to the documentation.

http://httpd.apache.org/docs/trunk/rewrite/remapping.html#fallback-resource

>    As of version 2.2.16, you should use the FallbackResource directive for this