Add spell-checking badge

Author: bbatsov

README.md

@@ -7,6 +7,7 @@
 [![MELPA](http://melpa.org/packages/cider-badge.svg)](http://melpa.org/#/cider)
 [![MELPA Stable](http://stable.melpa.org/packages/cider-badge.svg)](http://stable.melpa.org/#/cider)
 [![CircleCI](https://circleci.com/gh/clojure-emacs/cider.svg?style=svg)](https://circleci.com/gh/clojure-emacs/cider)
+[![Spell-check Status](https://github.com/clojure-emacs/cider/actions/workflows/spell_checking.yml/badge.svg)](https://github.com/clojure-emacs/cider/actions/workflows/spell_checking.yml)
 [![Discord](https://img.shields.io/badge/chat-on%20discord-7289da.svg?sanitize=true)](https://discord.com/invite/nFPpynQPME)
 [![Slack](https://img.shields.io/badge/chat-%23cider-green.svg?style=flat)](http://clojurians.net)