fix class documentation

lib/metasploit/framework/login_scanner/ssh_key.rb

@@ -5,9 +5,10 @@ module Metasploit
   module Framework
     module LoginScanner
 
-      # This is the LoginScanner class for dealing with the Secure Shell protocol.
+      # This is the LoginScanner class for dealing with the Secure Shell protocol and PKI.
       # It is responsible for taking a single target, and a list of credentials
-      # and attempting them. It then saves the results.
+      # and attempting them. It then saves the results. In this case it is expecting
+      # SSH private keys for the private credential.
       class SSHKey
         include ActiveModel::Validations