README: restore permissions escalation and PR invite lost in force push

Both lines were web edits (ea9192f) that a local force push overwrote.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

README.md

@@ -132,7 +132,9 @@ install-type archetype and prints the Ra build recipe.
 
 Members of the `unx-mx_adm` group can update `/opt/psi/MX` directly — no -adm
 account needed. Permission problems: Ask May/Meitian/Dawn to be added to 
-unx-mx_adm group.
+unx-mx_adm group. If you have been in the group for more than 48 hours and
+still can't write to /opt/psi/MX, ask the SLS beamline storage and compute
+admins (Email: sls-htc-admins@lists.psi.ch).
 
 ## Resources
 
@@ -140,6 +142,8 @@ unx-mx_adm group.
 - modbuild documentation: https://pmodules.github.io/modbuild/
 - Environment Modules: https://envmodules.io/
 
+If you want to provide more, feel free to submit a pull request to this document.
+
 ## Acknowledgements
 
 Many thanks to [Achim Gsell](https://www.psi.ch/en/lsm/people/achim-gsell)