Better document the Access Key url

The proper use of the Access Key setting can be obtuse.

For user's that unexpectedly lock themselves out, changing the module page intro text as described below could be quite helpful:

Prevent users from logging in to your Drupal site unless they know the secret key to add to the end of the ?q=user login form page.

to

Prevent users from logging in to your Drupal site unless they know the secret key to add to the end of the login form page. (default: http://yourwebsite.net/user/login?admin )