docs: correct submodule core support and add the CRM README

The Requirements section of the User and Group submodule READMEs listed Drupal core ^11.1, contradicting every .info.yml in the project — all of which declare '^11.1 || ^12' — and the base README. Drupal 12 support shipped in 1.0.0-alpha1, so a reader landing on a submodule README concluded that submodule was Drupal 11 only.

Both Requirements sections now read ^11.1 || ^12. Group and CRM also point at the base README's Drupal 12 limitations, since their own code is Drupal 12 ready but their phpunit (next major) job cannot pass while drupal/group and drupal/crm are incompatible — stating the constraint without that pointer would over-promise.

entity_segment_crm was the only submodule with no README; it now has one, modelled on the User submodule and carrying the same upstream caveat via drupal/crm and drupal:telephone.

No core_version_requirement is changed; those were already correct.

Closes #3612926