Update "docs" docs

[janbrasna]

The "Documentation" section still mostly implies this being part of bedrock repo:
https://mozmeao.github.io/platform-docs/install/#documentation

The setup commands no longer work, and should probably be replaced with some uv/venv steps relevant to this repo.

The link for listing issues still includes some tickets, but should also be updated to point here instead.

[janbrasna]

Also considering the main readme:

platform-docs/README.md

Lines 13 to 17 in d49dba7

	First, create and activate a virtual environment (using pyenv):
	```
	pyenv virtualenv 3.13.3 docs
	pyenv activate docs

to perhaps move to just plain vanilla venv without a specific Python version, as it should not make too much of a difference? (or, hinting at expecting using what's in the platform projects' current stack…) — as anything installed beyond that and pulling e.g. complete Python version installations like uv venv just for docs seems a little overboard.