Add more documentation links to section 8 pages

As kerberos(8) provides a brief outline of this network authentication
system I would suggest extending SEE ALSO to include a few section 8
commands.  I have excluded kadmind(8) and kpasswdd(8) as these servers
can be easily reachable from kadmin(8) and kpasswd(8) manual pages
respectively.

Signed-off-by: Love Hornquist Astrand <lha@h5l.org>