mailman: add header for direct linking

mail/mailman/create_account.markdown

@@ -29,6 +29,8 @@ Given that mailing lists may be public and used by external users, the service i
 
 [[!img /media/mail/mailman/signup_6.png size="550x"]]
 
+### Manage additional email addresses
+
 * You may optionally link additional emails to your mailman account. This is useful if you also want to send messages using any of your email aliases.
 
 [[!img /media/mail/mailman/signup_7.png size="550x"]]