fabric: add README (#7378)

plugins/fabric/README.md

+# Fabric
+
+This plugin provides completion for [Fabric](https://www.fabfile.org/).
+
+To use it add fabric to the plugins array in your zshrc file.
+
+```bash
+plugins=(... fabric)
+```

plugins/fabric/fabric.plugin.zsh

-# DECLARION: This plugin was created by vhbit. What I did is just making a portal from https://github.com/vhbit/fabric-zsh-autocomplete.