gen-markdown generator, for docs generation

[pkieltyka]

related to #246

once we have comments in our schema, we can generate pretty decent documentation from a webrpc schema definition (in either ridl or json of course, since they're the same just different formats).

I've added https://github.com/webrpc/gen-markdown which we can use to parse a single schema file, and output a markdown contents, which can be piped into a file, or can be used in a pipeline for example with any static site docs generator (ie. docusaurus, vocs.dev, etc. etc.), and then it makes it easy to have a "API Reference" section in docs which are generated by this gen-markdown with comments coming from the schema.

[VojtechVitek]

I found this OpenAPI->Markdown generator:

$ webrpc-gen -schema=./test.ridl -target=openapi -out=test.gen.yaml

$ docker run --rm -v "${PWD}:/app" openapitools/openapi-generator-cli:v6.2.1 generate -i /app/test.gen.yaml -g markdown -o /app/test.md

It might do what we need for now.