x/pkgsite: improve package notes headers

[rekby]

What is the URL of the page with the issue?

https://pkg.go.dev/sync/atomic

What is your user agent?

Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/15.4 Safari/605.1.15

Screenshot

What did you do?

Open document page

What did you expect to see?

I expected to see separator and headers similar to "Package notes".

What did you see instead?

Now I see header "Notes" and my first thing about notes related to function "func (*Value) Swap" (not all package) and the Swap function has bug.

[jamalc]

/cc @jinhongy

[jinhongy]

Here are a few comments from design perspective:

1. There should be a bug on clicking 'Notes" seems it expanded the functions when I click it.
2. Thats a great idea to have "Notes" as a separate section. Before doing this change, there is one thing we should take into consideration: Is "Package Notes" a session most other docs would have or for this package only? We have the separator under session title like " Source files" in the captured screen. If most other package docs have the same session, then we can add a new session for "Notes" . If "Note" is for this package only, then I would recommend not adding new pattens here.

[beRajeevKumar]

I think there is no need to write any "Notes" over there.
We can simply put an emoji like 👉🏻 or any icon which marks it as an important condition like this ❗️, ⚠️, or any similar icon.
But if this occurs on every documentation page then think about a new idea of the design.