Add documentation for detectable breaking/non-breaking changes

[kylerjensen]

We are using this library to power a GitHub Action that generates a backward compatibility report between two versions of an OpenAPI spec. We love this library, but it is not clear what changes are detectable by this library, and what changes this library classifies as "breaking" or "non-breaking" changes. It would be really valuable to us if this repo could include a markdown file outlining all the OAS changes that this library can detect.

[mpokryva]

This would be really great. I'd like to use this tool, but I have no idea if I'd need to extend it to fit my use case. Is there any plan to write docs for this?