feat(cli): add 'doom make completions' for zsh

'doom make completions' will generate a rudimentary ZSH completion
script for bin/doom. It can be used from your shell dotfiles, but I
recommend caching the output with a function like:
https://github.com/hlissner/dotfiles/blob/master/config/zsh/.zshenv#L1-L14.

Then add this to your .zshrc:

  _cache doom make completions --zsh && compdef _doom doom

Ref: https://github.com/hlissner/dotfiles/blob/master/config/zsh/.zshenv#L1-L14

bin/doom

@@ -277,7 +277,7 @@ SEE ALSO:
     (defgroup! "Development"
       :docs "Commands for developing or launching Doom."
       (defautoload! (ci))
-      ;; TODO (defautoload! (make))
+      (defautoload! (make))
       (defautoload! (run))
 
       ;; FIXME Test framework