Add documentation to Invite feature (#636)

Author: phavekes

roles/invite/templates/serverapplication.yml.j2

@@ -133,6 +133,7 @@ config:
 
 feature:
   enable-performance-seed: False
+  # Allow non-eduID accounts to accept invites for rolemanager and inviter
   allow-for-eduid-only-enforcement-for-non-guests: False
 
 # We don't encode in-memory passwords, but they are reused so do NOT prefix them with {noop}