Looks great! Hope you'll forgive the copy-editing suggestions.
#7 in the list could be "Include links to other content when necessary," and point to how/where to find those. I don't know whether these descriptions support links, so I'll leave that to you to include if it's worthwhile.
You might also note that it's helpful to indicate in the description for a request header/query parameter whether it is required or optional.
I'm not sure what "the Linter" is, although I heard you say it the other day, so that might be good to define here.
First pass at pull request template
Adding contribution documentation in CONTRIBUTING.md
Adding pattern in documentation for links back to the adx-documentation-pr repo
Since JSON is very strict about comments and non-JSON characters, Github does some ugly highlighting when using `...` to represent omitted lines in our documentation. By switching to the `json5` hint for large code blocks, it's a little easier to read.
This is only a documentation formatting change. It has no impact on the specs in this repo.