Continue to refactor the contributing guide

[psobolewskiPhD]

🧰 Task

The following PR is a nice improvement:
#761

But there are still more things that could be done.
At the docs meeting, we discussed possibilities:

1. remove the bullets for the Core Dev Guide info and move it to just text below the card, since more visitors will be contributors rather than core devs. The bullets duplicate the toc
2. if 1. is done, then it may be possible to layout the remaining contributor things into clickable cards like plugins!

[DragaDoncila]

Another point would be to add the deploying docs page to the TOC for core dev guide.

@TimMonko let us know what you think of the current improved version after #761 and what you think of the suggestions here!

[TimMonko]

It looks great! On 1, that sounds good, on 2, that also sounds good
I would potentially add 3, though it's a separate issue: we pull the entire contributing docs section into its own parent, because its a) getting quite long, and b) is really valuable and complete!