go/doc: find a better home for Go documentation features like section headings

[matttproud]

fluhus/godoc-tricks describes several extended tricks for the Godoc renderer that remain relevant for https://pkg.go.dev. Particularly notable is the technique described as Titles, which can be thought of as naive section headings as demonstrated below with the word "Limitations":

// CreditCard models a lender-backed payment instrument.
//
// Limitations
//
// The type provides no native validation against its issuer.  It is a dumb data type.
type CreditCard struct{}

To date this technique is not substantively mentioned in any of the following:

• https://blog.golang.org/godoc
• https://golang.org/pkg/go/doc/ (minor prosaic allusion)

Considering its utility for information presentation, anchoring, etc., I propose the feature earn proper documentation. I tried to search for an existing bug for this, but the closest thing I could find was #18342. The correct approach would probably involve amending the previous documents somehow (or maybe another).

[dmitshur]

I'll highlight the current documentation at https://golang.org/pkg/go/doc/#ToHTML:

Each span of unindented non-blank lines is converted into a single paragraph. There is one exception to the rule: a span that consists of a single line, is followed by another paragraph span, begins with a capital letter, and contains no punctuation other than parentheses and commas is formatted as a heading.

If we had documentation about writing documentation (similar to https://blog.golang.org/godoc, but as evergreen documentation rather than a blog post), I agree this should be covered there. I don't know if there are plans to do this at this time.

CC @julieqiu, @stevetraut, @griesemer.