Add reference gist for Qt guest mode stuff

piker/ui/_exec.py

@@ -99,6 +99,9 @@ def run_qtractor(
     # "This is substantially faster than using a signal... for some
     # reason Qt signal dispatch is really slow (and relies on events
     # underneath anyway, so this is strictly less work)."
+
+    # source gist and credit to njs:
+    # https://gist.github.com/njsmith/d996e80b700a339e0623f97f48bcf0cb
     REENTER_EVENT = QtCore.QEvent.Type(QtCore.QEvent.registerEventType())
 
     class ReenterEvent(QtCore.QEvent):