Add donation link to “Website Under Heavy Load” page

An error page made it to socials, and it’s a perfect opportunity to encourage people to donate.

Perhaps something like:

_Whoops - we are super popular at the moment! Please consider donating so we can keep this essential service running!_

See social post here:
https://github.com/user-attachments/assets/ff7e526b-7a97-4b6f-bcee-a659d1fc835a
