adding some information about plugin

plugins/administrator/INSTALL

@@ -1,6 +1,6 @@
 Administrator Plugin
 --------------------
-2002 Philippe Mingo <philippe@squirrelmail.org>
+Author: Philippe Mingo <philippe@squirrelmail.org>, 2002
 
 In order to use this plugin, you must first activate it using
 conf.pl and then you must change the config/config.php files
@@ -12,7 +12,17 @@ work, if user's id equals to 0.
 
 An alternative method, but less secure, is to add a file called
 admins into the plugin folder with the names of the users that
-you want to allow the use of the plugin.
+you want to allow the use of the plugin. admins file must have 
+empty line after administrator's username. If administrator name
+ends of end-of-file symbol instead of line feed, it will be 
+ignored.
 
 Use this plugin at your own risk, and always remember to make a
 backup of your config.php file before use. 
+
+Order of authentication checks
+------------------------------
+When plugin checks if user can use it, it first checks 
+plugins/administrator/admins file. If file does not exist, plugin
+checks config/admins. If plugin can't find admins file, it tries to
+use uid based authentication.