capistrano: add README (#7376)

plugins/capistrano/README.md

+# Capistrano
+
+This plugin provides completion for [Capistrano](https://capistranorb.com/).
+
+To use it add capistrano to the plugins array in your zshrc file.
+
+```bash
+plugins=(... capistrano)
+```
+
+For a working completion use the `capit` command instead of `cap`, because cap is a
+[reserved word in zsh](http://zsh.sourceforge.net/Doc/Release/Zsh-Modules.html#The-zsh_002fcap-Module).
+
+`capit` automatically runs cap with bundler if a Gemfile is found.

plugins/capistrano/capistrano.plugin.zsh

-# Added `shipit` because `cap` is a reserved word. `cap` completion doesn't work.
+# Added `capit` because `cap` is a reserved word. `cap` completion doesn't work.
 # http://zsh.sourceforge.net/Doc/Release/Zsh-Modules.html#The-zsh_002fcap-Module
 
-func capit() {
+function capit() {
   if [ -f Gemfile ]
   then
     bundle exec cap $*