Buf plugin example

[dv-stewarts]

I wanted to make it easier for people to understand how to use the api-linter as a buf plugin, so I created an example project using the bookstore example.proto (Which embarrassingly fails linting) and added an explanation to the docs.

I also updated some stale references and text in the docs which still referred to AIP pages.

[toumorokoshi]

Which embarrassingly fails linting

Did you import the aeps example, or the aepc example?

The aepc example is fully compliant - so perhaps if you pulled in the aeps one I can send a PR to update that one.

[toumorokoshi]

LGTM, sans the one comment on .gitignore. Once that's addressed I'm happy to do the merge. Thank you!

[dv-stewarts]

Did you import the aeps example, or the aepc example?

The aepc example is fully compliant - so perhaps if you pulled in the aeps one I can send a PR to update that one.

It was the aeps example. I've updated with the one from aepc and that does, indeed, pass. I think it's worth updating the example to ensure compliance.