README: point questions at Bluesky (no sign-ups here)

Co-Authored-By: Claude Opus 5 <[email protected]>

README.md

@@ -5,6 +5,10 @@ board that also carries the USB hub. One cable reaches the computer.
 
 Status: **design**. No boards ordered, no firmware written.
 
+Questions, corrections or bug reports: **[ask on Bluesky](https://bsky.app/profile/tangentheavy.com)**
+([@tangentheavy.com](https://bsky.app/profile/tangentheavy.com)). Sign-ups on this git server are
+closed, so there are no issues to file here.
+
 ![All three boards to scale](Documents/three-board-overview.svg)
 
 <table>