0x1209: add 0x7EAD PID (TheadMouse)

Signed-off-by: Martin Pietryka <martin@pietryka.at>

Author: pietrmar

1209/7EAD/index.md

@@ -0,0 +1,9 @@
+---
+layout: pid
+title: TheadMouse
+owner: pietrmar
+license: GPL-3.0-or-later, CERN-OHL-S-2.0
+site: https://theadmouse.com
+source: https://github.com/pietrmar/theadmouse
+---
+The TheadMouse is an open-source IMU-based head-tracking mouse designed for people with disabilities.