Note recommended Ruby version

Author: twilco

README.md

@@ -9,6 +9,8 @@ Welcome!  This repository houses the code for [my blog](https://twilco.github.io
 3. Use bundler to install packages required for the project - `bundle`
 4. Use Jekyll to serve the site at [localhost:4000](http://localhost:4000) - `bundle exec jekyll serve`
 
+[GitHub pages doesn't seem to be compatible with Ruby 3 yet](https://talk.jekyllrb.com/t/error-no-implicit-conversion-of-hash-into-integer/5890), so using a Ruby version manager like [rbenv](https://github.com/rbenv/rbenv) to run Ruby 2.7.3 for this repository is recommended.
+
 Feel free to open an issue or PR for anything you find that needs fixing, or if you enjoyed a specific post and want to see more like it.
 
 <https://twilco.github.io>