- main README: add Pmodules background from wiki, unx-mx_adm group
replaces -adm account for updating modules in /etc/psi/MX, and
how to propagate main to the build-* tutorial branches
- module READMEs: fix titles/paths to match module directories
(DIALS, jfjoch_viewer), replace -adm login steps with unx-mx_adm note
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>