Add description to all HTML/SVG attributes with ocaml.doc

[davesnx]

Each prop might contain a small description of itself, that we could provide to the user. Which would be great to have as documentation on your editor with the hover (with ocaml.doc).

Plus would be a really complete feature if we have a documentation page for it.

[jchavarri]

This will be much much easier with new api, e.g.

not sure if it would make sense to do it before or after #136 🤔 or order does not matter.