add UIDGID comment

Author: gilesknap

docs/explanations/rootless.md

@@ -25,6 +25,7 @@ At present epics-containers requires slightly different configuration for docker
 - Permissions on the files inside the developer container need to be set with *sudo chown* at startup
 - Developer containers will sometimes have issues with git repo permissions
 - docker compose deployed IOCs do run as root and write any generated files as root in host mounted folders (this needs fixing)
+- UIDGID is required to be passed to the compose file for phoebus to make sure it runs as the correct user (but would not be needed at all for rootless)
 
 ## Proposed solution
 
@@ -36,6 +37,8 @@ This would therefore be accetable if it is easy to switch between rootfull and r
 
 ## Configure Docker with rootless/rootfull operation
 
+Note that some fixes to epics-containers 'Current Situtation' are required if you switch to rootless operation - we can remove some of the config requirements.
+
 These instructions worked for me on Ubuntu 24.04. Assume docker default install is already done and is at version 27.2.0.
 
 1. docker install comes with a script to set up rootless operation. We use --force to tell it to run even though rootfull is already set up.