added clarification to ssh user changes

CHANGELOG.md

@@ -309,7 +309,7 @@ newline being stripped you can change your playbook like this:
 * new managed_syslog option has been added to control output to syslog on managed machines, no_log supercsedes this settings.
 * Lookup, vars and action plugin pathing has been normalized, all now follow the same sequence to find relative files.
 * We do not ignore the explicitly set login user for ssh when it matches the 'current user' anymore, this allows overriding .ssh/config when it is set
-  explicitly. Leaving it unset will still use the same user and respect .ssh/config.
+  explicitly. Leaving it unset will still use the same user and respect .ssh/config. This also means ansible_ssh_user can now return a None value.
 
 ## 1.9.4 "Dancing In the Street" - Oct 9, 2015