Add information about global route patterns

This is a really nice feature (which I learnt about from [Aaron Kuzemchak's post](http://kuzemchak.net/blog/entry/laravel-quick-tip-global-route-constraints) last week) that lets you set global regular expressions for all your routes:

    Route::pattern('id', '\d+');
    Route::pattern('slug', '[\da-z-]');
    // etc.