Remove Readme from adaptor docs

[josephjclark]

The README section of the adaptors docs is, by and large, no longer useful.

Since moving to the monorepo the readmes are pretty terse. The only valuable stuff is the contribution and source links, and why not just expose those more clearly for each adaptor?

Usage guides and tutorials and stuff which the readmes may contain would be better presented in the overview, examples, or even their own section.

Instead of the readme, we should add a Contributing & Feedback. This would be boiler-plate for each adaptor with links to the monorepo, basic a check out instructions, github issues etc.