For specific subsections, TG has some introductory paragraphs, i.e. at https://core.telegram.org/bots/api#games. These are currently not available directly in the PTB docs.

We should

1. add them to the PTB docs (e.g. above paragrph to https://docs.python-telegram-bot.org/en/v21.4/telegram.payments-tree.html)
2. Revisit all "More info on xy »" links and make them point to the PTB docs where possible .That way, users don't have to jump between PTB and TG docs

Context:
Proposed by @Poolitzer in dev chat