Add `copy to clipboard` to code examples in `charm-ruby.dev` site

[binarygit]

I thought it'd be a good idea to add a copy to clipboard buttons for the code examples in the charm-ruby site.

Happy to take this on myself if you think it's a good idea 😅
I couldn't find the source code for the site in your repositories which is why I opened an issue here. I hope that's okay.