docs(readme): add 'commits since latest release' badge

Author: olets

README.md

@@ -1,6 +1,6 @@
 <img src="./img/git-prompt-kit.png" alt="">
 
-# Git Prompt Kit ![GitHub release (latest by date)](https://img.shields.io/github/v/release/olets/git-prompt-kit)
+# Git Prompt Kit ![GitHub release (latest by date)](https://img.shields.io/github/v/release/olets/git-prompt-kit) ![GitHub commits since latest release (by SemVer including pre-releases)](https://img.shields.io/github/commits-since/olets/git-prompt-kit/latest)
 
 **Git Prompt Kit** is a configurable set of components for creating feature rich, high performance Git-aware zsh prompts (aka themes) with minimal coding. It is built on gitstatus, the same accelerated `git status` alternative used by Powerlevel10k.