Update the README.txt file

Could you please also add something like this to the documentation while you're updating it for other newcomers to this wonderful module. If you want me to make a patch file I will, but hopefully this will suffice.

At the end of the == Installation == section, please add:

Be sure and run update.php after enabling this module, it is needed.

== Usage ==

If you are logged in as a user with permissions to use Masquerade, you can switch to any other user by visiting the url
http://sitename/masquerade/switch/. You will find a link to this url if you visit the user's account page at http://sitename/user/ which you can get to via the Drupal user administration.

Once you log in as this alternate user, you will see a one-time message at the top of the screen indicating that you have logged in as this other user. You can then revert back to your original user account by clicking on the new link that appears in the navigation menu, if you have this menu enabled on your site, or by going to the http://sitename/masquerade/unswitch link.