Merge branch 'explain_allow_username_or_email_login' into 'master'

Explain allow_username_or_email_login LDAP setting

config/gitlab.yml.example

@@ -127,6 +127,11 @@ production: &base
     method: 'ssl' # "ssl" or "plain"
     bind_dn: '_the_full_dn_of_the_user_you_will_bind_with'
     password: '_the_password_of_the_bind_user'
+    # If allow_username_or_email_login is enabled, GitLab will ignore everything
+    # after the first '@' in LDAP the username submitted by the user on login.
+    # Example:
+    # - the user enters 'jane.doe@example.com' and 'p@ssw0rd' as LDAP credentials;
+    # - GitLab queries the LDAP server with 'jane.doe' and 'p@ssw0rd'.
     allow_username_or_email_login: true
 
   ## OmniAuth settings