x/website: add alphabet shortcuts

[ujukiSakuta]

Can you add alphabet shortcuts in packages page?
Something like this
https://imgur.com/6wdIcaX

[ALTree]

In which pages, and pointing to what? The package's functions? Note there's a TOC on the left.

[gopherbot]

Timed out in state WaitingForInfo. Closing.

(I am just a bot, though. Please speak up if this is a mistake or you have the requested information.)