manuals: Fix some .Bl -tag lists

Signed-off-by: Graham Percival <gperciva@tarsnap.com>
Reviewed by: mhorne, Alexander Ziaee <concussious.bugzilla@runbox.com>
MFC after: 3 days
Sponsored by: Tarsnap Backup Inc.
Pull Request: https://github.com/freebsd/freebsd-src/pull/1528