Add documentation of "Doc comments" (and non-doc comments)

[mikekistler]

TypeSpec supports JS Doc style comments as an alternative (and preferred) to @doc.

But I don't think this is documented in the public docs. What's more, I also don't see normal comments ("//") documented anywhere.

I think both of these should probably be added as a section in the "Language Basics / Overview" page.

https://microsoft.github.io/typespec/language-basics/overview

[markcowl]

est: 3