Promote uv in installation guides (#14056)
> [Because this is an Astral repository
;)](https://github.com/astral-sh/packse/pull/183)
[Originally
reported](https://discord.com/channels/1039017663004942429/1039017663512449056/1302319421204729906)
by clearfram3 on Discord.
`grep`ping for `pip install` in `.md` files reveals a few other places
where the same fix might be applicable.
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Co-authored-by: Micha Reiser <micha@reiser.io>
