Small Documentation improvements

[SimonDanisch]

• make funding, citating Makie and makie.org more visible (put it in the banner?)
• Add some words about how to reach us and what form of communication/help can be expected (I think this needs to be a small document we link, maybe also in banner)
• Put the ecosystem overview from https://makie.org into the end of the start page, to give a better idea of what can be done with Makie (I think this is pretty important, because its really hard to judge if Makie is usabel for X, without a broad overview of capabilities).
• Maybe also add the Supporter section to the docs

[DanielVandH]

Wasn't there a Makie showcase/gallery somewhere? That would be another good thing to show/at least link to somewhere to complement your third point. (Actually I also forgot there was an ecosystem overview on makie.org, the one at https://docs.makie.org/stable/ecosystem is quite empty atm.)