Minor update to check if application is under maintenance documentation

While reading through the documentation in public/index.php, the initial
sentence documenting checking if the application is under maintenance
didn't quite read properly to me, nor did the section's header. So, I'm
submitting this small patch to correct it.

public/index.php

@@ -7,11 +7,11 @@
 
 /*
 |--------------------------------------------------------------------------
-| Check If Application Is Under Maintenance
+| Check If The Application Is Under Maintenance
 |--------------------------------------------------------------------------
 |
-| If the application is maintenance / demo mode via the "down" command we
-| will require this file so that any prerendered template can be shown
+| If the application is in maintenance / demo mode via the "down" command
+| we will require this file so that any pre-rendered template can be shown
 | instead of starting the framework, which could cause an exception.
 |
 */