Include tip in README to disable Apache's handling of PHP files

[rdlugosz]

It seems that Apache will preempt your Rails app and any associated redirects created with rack-rewrite if the PHP handler is enabled & the request url is for something like "/contact.php".

Not really an issue with rack-rewrite, but since redirecting php scripts is the first example use case in the readme, it seems worthwhile to mention that you need to include the following directive either in the VirtualHost section of httpd.conf or in an .htaccess file in the root of your app's public directory:

php_flag engine off