homestead: add README (#7343)

plugins/homestead/README.md

@@ -0,0 +1,9 @@
+# Homestead
+
+This plugin provides completion for [Homestead](https://laravel.com/docs/homestead).
+
+To use it add homestead to the plugins array in your zshrc file.
+
+```bash
+plugins=(... homestead)
+```