service.8: Provide example for adding completions to (t)csh
service(8) has an example for bash completion, however bash is third
party and in /usr/share/examples/csh/dot.cshrc is a working example for
Since I use (t)csh, I've tested it, and it works for me.
Submitted by: ohauer@
Reviewed by: kp (tentatively)
Differential Revision: https://reviews.freebsd.org/D28197