Add more sponsors

[NitramLegov]

We should think about which supporting organizations we can add to our sponsors page.

This includes getting an (ideally written) approval from them to include the logo in our site.

[LukasFreeze]

I'd say this is not necessary for "version 1" - besides just getting some logos, shouldn't we actually get sponsorship?! That is definitely a goal, but will almost definitely take longer than the new website should have to wait.