Title: #5279: man: clarify AD certificate rule
Clarify AD specific certificate rule example by changing userPrincipal to
userPrincipalName. Moreover, match the subject principal name in the
example with the rule name.
To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/5279/head:pr5279
git checkout pr5279