Triage .md files

[ggwpez]

There are a few .adoc files in the workspace - most of them looking rather unuseful.
I think we should either remove them or fix and convert to markdown with some tool so we can use MD tooling eventually #1243.

cc @paritytech/docs-audit (not sure if you are the right to mention here?!)

[kianenigma]

I would no-brainer say remove all .adoc and .md files that are acting as code doc, and instead replace them as rust-doc.

We should double down on rust-doc and encourage everyone to read those.

Also in the spirit of #991

[ggwpez]

Actually all adoc were removed in #1382, but there are still oneliner README files so going to change that title here.

[kianenigma]

Now that we are releasing to crates.io, we should make sure we remove all these files, and run https://docs.rs/crate/cargo-markdown/1.0.3 as a part of our of release to crate.io process.

[ggwpez]

Or try this tool? https://github.com/webern/cargo-readme The cargo-mardown from above looks like it only previews things instead of also generating.

So we probably want a script that does this for all crates and then trigger it once before each release.
@Morganamilo is there a pre-release checklist or something where we could add this as item?