compsys: Adding completions

This will replace the default completion (files) with hosts, for the command sshx (which is a custom script)

compdef _hosts sshx

To complete on only some type of files (ex: *.gp) you can do:

compdef '_files -g "*.gp"' gnuplot

Perhaps you use some new program, say ninja, and zsh has no _ninja completer for it.
If ninja accepts a –help option, you can try using _gnu_generic as a completer for it:

compdef _gnu_generic ninja