Donate button

A few months ago, I put in a [PR](https://github.com/carpentries/workshop-template/pull/894) to add a "Donate" link to the navbar. A button and/or callout would have been better, but the old layout was a bit clunky.
With our new styles, it would be much easier to do this. I am opening this issue to get feedback on where the button should go in the new layout. Perhaps another card like the existing Carpentries Clippings and CoC cards on the right side of the about The Carpentries card?

Tagging @OscarSiba and @elletjies for feedback.

[Preview the layout](https://carpentries.github.io/workshop-template/).

Review the linked preview layout, especially the navbar and the existing Carpentries Clippings and CoC cards beside the About The Carpentries card. The issue first needs feedback and agreement on placement; done means the agreed Donate button or callout is present in the new layout.

Written by the indexing model from the issue text.