Rethink release process and document it

[brendanzab]

Managing monorepos can sometimes be tricky! I've been trying to keep a single version between codespan-reporting, codespan, and codespan-lsp, and have been manually tagging + writing release notes, but unfortunately hadn't documented or communicated this process. It also ends up being a bit of work. And if I merge breaking changes into the main branch it means I need to do extra work if I get PRs for non-breaking changes, say, updating the version bounds of codespan-lsp.

I was a bit overwhelmed with stuff this past several weeks and @Marwes helpfully stepped in. This was most appreciated 😍, and why I add people as maintainers! But I'd not communicated the above process I was doing, so my current approach is now a bit messed up. So perhaps we can use this as a time to rethink our approach!

@Kixiron pointed me to cargo-release which looks handy for managing crate releases in cargo workspaces - perhaps we could use this to make our lives easier? 🤔 I'm also thinking it might be worth documenting the release process in a CONTRIBUTING.md file, or something like that.