docs: Reorganize the "Development" section

[MarieSacksick]

Closes #1582

This issue says three things:

1. We might also consider reformatting a bit the Development outline if needed.
2. Also would it make sense to rename this to just "Contributing"? Since the context is already within the skrub repo, "Contributing to skrub" might be a bit redundant. (I agreed, and therefore did the change)
3. we can start by removing "Contributing to skrub" from the drop down menu, since it's already present in the "Development" page.

2 and 3 are tackled.
For 1, I quite like the contributing guide for now, because it's very detailed. Most of what I did is changing from:

to:

The idea is to go step by step for the contributor. Building the doc locally to me is part of checking the quality of contribution.

[MarieSacksick]

this is actually unclear to me: isn't it this instead, since there is a mention of community?

Suggested change

	of 1 to 3 reviews depending on the size of the change before we consider
	of 1 to 3 reviewers depending on the size of the change before we consider

[rcap107]

I would rather have something like "Expect a minimum of 1 to 3 reviews from maintainers..."

[MarieSacksick]

Given the number of warnings already present, I think it's very hard check to do and to enforce.
Shouldn't it be removed?

Suggested change

	**Before submitting your pull request, ensure that your modifications haven't
	introduced any new Sphinx warnings by building the documentation locally
	and addressing any issues.**

[MarieSacksick]

Or, other solution would be to create a couple of issues to fix the current warnings in documentation building.

[rcap107]

We can do both. From experience silencing all the sphinx warning would be nigh impossible, so I think it makes sense to remove this sentence.

[rcap107]

This looks good! Thanks a lot @MarieSacksick 👍

I left a couple of comments, but aside from that I think it's already a big improvement

[rcap107]

I think this can be removed

[rcap107]

I would rather have something like "Expect a minimum of 1 to 3 reviews from maintainers..."

[rcap107]

This looks good! Thanks a lot @MarieSacksick 👍

I left a couple of comments, but aside from that I think it's already a big improvement