Add migration story for LDAP UUID home directories

docs/release-notes.rst

@@ -22,6 +22,9 @@ NixOS 26.05
   established by `agenix`_/`sops-nix`_ that instead rely on encryption. This
   option prevents files from leaking in to the Nix store.
   See :option:`mailserver.loginAccounts.<name>.passwordFile`.
+- LDAP setups require a migration of Dovecot home directories to
+  `UUID based home directories`_. The exact UUID attribute can be customized
+  through :option:`mailserver.ldap.attributes.uuid`.
 - The default login username for LDAP users has changed from the ``mail`` to
   the ``uid`` attribute. This allows users to login with their account name
   rather than their email address, which is more convenient and consistent
@@ -38,6 +41,7 @@ NixOS 26.05
 .. _DKIM key management: dkim.html
 .. _agenix: https://github.com/ryantm/agenix
 .. _sops-nix: https://github.com/Mic92/sops-nix
+.. _UUID based home directories: migrations.html#dovecot-ldap-uuid-based-home-directories
 
 NixOS 25.11
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