Let people know about our Flattr account

Once we configured and advertise our Flattr account, we should let people know about it. That could mean tweeting only, writing a short blog post, etc.

Related issues

Related to #12486 (closed)
Blocked by #10045 (closed)

Original created by @sajolida on 10186 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information