Add a copy button for code snippets in the docs

[edrogers]

Since the Quick Start kicks off with a 14 line snippet of code to copy-paste, it would be nice to have a copy-to-clipboard button handy. (GitHub provides one by default with code blocks, but mkdocs material theme requires a feature to be enabled in the theme for this.)

I'll make a quick PR for your consideration here

[JoshKarpel]

That'd be fantastic @edrogers - great idea, and I'm always happy when it turns out the material theme already has the feature! 😁