Collect end-user donations using Liberapay #462

Our Liberapay team is a thing now (see forgejo/governance#148) and I'd appreciate if it could be linked from the website.

I don't mind if it's just in the footer or if it's a prominent "Donate" button. The latter would likely bring us more funding.

Potential positions:

• top navbar (likely the best effect)
• action buttons on the hero ("Get Forgejo", "Try Now", + "Donate"), likely efficient but maybe a little irrelevant there
• below "Get involved", next to "Contribute on Codeberg", not as prominent but probably still good. It's not directly related to contribution, but "Fund the development" or "Become a financial backer" would still fit there
• in the footer only

I think navbar and the "Get involved" sections are my personal preferences.

Another idea that came to my mind, but I'm not yet sure if I like it:

extend the two column section with Forgejo features and add two more:

• open governance, decision making etc
• transparently funded, grants, donations ...