added a few lines in the documentation

Author: Erwin Dondorp

README.md

@@ -70,6 +70,12 @@ SaltGUI supports the following authentication methods supported by salt:
 - mysql
 - yubico
 
+Since pam by itself is already very powerfull, that one is mentionned as standard.
+By default, it provides access to the Linux password file,
+When other authentication methods need to be used their names can be added to file `saltgui/static/salt-auth.txt`.
+There is one name per line in that file. Choose the authentication methods that are activated
+in the salt-master configuration wisely, as the integrity of the salt-master and all salt-minions depends on it.
+
 See the [EAUTH documentation](https://docs.saltstack.com/en/latest/topics/eauth/index.html) and the [Salt auth source code](https://github.com/saltstack/salt/tree/master/salt/auth) for more information.
 
 ## Command Box