Add documentation on platform dependencies

[helhum]

No description provided.

[helhum]

Updated version of #9965

[naderman]

Thanks for the docs, I know I edited a lot, but really wouldn't have been this easy if you hadn't already provided all the content ;-)

[naderman]

Eh I see Jordi didn't wait for me to actually review as he asked, so my changes conflict with some of his. So ideally revert whatever @Seldaek tweaked in the docs and then just apply my suggestions?

[helhum]

Thanks for the doc updates. I can now take care integrating them cleanly, resolving the conflicts. What I wasn't able to figure out is what PHPStan's complaint is about. So that will be something you'll need to fix in the end.

[helhum]

@naderman I integrated your suggestions now (thanks all of them made a lot of sense), merged with @Seldaek changes where applicable and fixed some additional typos that I found after that.
Since PHPStan is also happy now, I think this is good to go as well?

[naderman]

@helhum great thanks!

[Seldaek]

Thanks everyone!