docs: user/getting_started: add dependencies

[herbetom]

Changing the docs as well was missed in b1cdcc8

Reported-in: #3414
Reported-by: 132701936+ChristianMiddendorf@users.noreply.github.com

[herbetom]

Rendered version appears to look fine: https://gluon--3424.org.readthedocs.build/en/3424/user/getting_started.html#dependencies

[blocktrron]

Please refer the dockerfile in the documentation instead of duplicating.

I also assume one would rather want a install command he can just copy and paste.

[AiyionPrime]

Just a general minor gesture, but I'd try to add Christian as author of the commit, if it's his contribution.
Feel free to add yourself as a co-author or the other way around, so that others can infer whose idea this was by looking at the git log :)

This might show a little more appreciation for the work they've put into spotting this.

[herbetom]

I think i added Christian as "Reported-" because i took the idea of fixing that from there but didn't actually use those changes and with the commit message also not beeing what we need i didn't really felt comfortable authoring that in someone elses name. But adding a "Co-Authored-By" seems like a good idea.

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Regarding referring to the Dockerfile: I'm not going to look into that further because while it seems like a sensible idea it either would be something without a link (which also isn't that user friendly) or it would probabbly end up pointing to the main branch (at least I can't think of a good way to make the link dynamic) which also would be supoptimal. So in that regard it's a "take it or leave it" regarding my involvement 🙈