Feature: Add FreeCAD Shop link

### Feature description

See https://forum.freecad.org/viewtopic.php?t=107348

It would be cool to have the merch shop linked somewhere:
https://shop.freecad.org/

### Feature implementation

Maybe link to the shop from on the community page or small hint under donations.

BTW there is a typo on the donation page

Locate the community and donation page content or templates in the Hugo website and inspect the donation-page text shown in the attached image. Add a visible link to https://shop.freecad.org/ in an appropriate location and correct the reported donation-page typo; done means both pages render correctly and the shop link works.

Written by the indexing model from the issue text.