git-flow-avh: add README (#7360)

plugins/git-flow-avh/README.md

+# git-flow (AVH Edition) plugin
+
+This plugin adds completion for the [git-flow (AVH Edition)](https://github.com/petervanderdoes/gitflow-avh).
+The AVH Edition of the git extensions that provides high-level repository operations for [Vincent Driessen's branching model](https://nvie.com/posts/a-successful-git-branching-model/).
+
+To use it, add `git-flow-avh` to the plugins array in your zshrc file:
+
+```zsh
+plugins=(... git-flow-avh)
+```
+
+## Requirements
+
+1. The git-flow tool has to be [installed](https://github.com/petervanderdoes/gitflow-avh#installing-git-flow)
+   separately.
+
+2. You have to use zsh's git completion instead of the git project's git completion. This is typically
+   done by default so you don't need to do anything else. If you installed git with Homebrew you
+   might have to uninstall the git completion it's bundled with.

plugins/git-flow-avh/git-flow-avh.plugin.zsh

-#!zsh
-#
-# Installation
-# ------------
-#
-# To achieve git-flow completion nirvana:
-#
-#  0. Update your zsh's git-completion module to the newest version.
-#     From here: https://github.com/zsh-users/zsh/blob/master/Completion/Unix/Command/_git
-#
-#  1. Install this file. Either:
-#
-#     a. Place it in your .zshrc:
-#
-#     b. Or, copy it somewhere (e.g. ~/.git-flow-completion.zsh) and put the following line in
-#        your .zshrc:
-#
-#            source ~/.git-flow-completion.zsh
-#
-#     c. Or, use this file as a oh-my-zsh plugin.
-#
-
 _git-flow ()
 {
     local curcontext="$curcontext" state line