* gnu/services/sddm.scm (sdm-pam-service): Set uid from CONFIG.
(sdm-autologin-pam-service): Set uid from CONFIG.
(sdm-pam-services): Pass CONFIG to 'sddm-pam-service' and
'sddm-autologin-pam-service'.
* doc/guix.texi (X Window): Adjust 'minimum-uid' documentation.
Co-authored-by: Ludovic Courtès <ludo@gnu.org>