Add comment for turret position conventions

Change-Id: I28d3f569810d229f145c261c3e18f510011af020
Signed-off-by: James Kuszmaul <jabukuszmaul+collab@gmail.com>
diff --git a/y2022/control_loops/superstructure/superstructure_position.fbs b/y2022/control_loops/superstructure/superstructure_position.fbs
index ac6f094..46dd547 100644
--- a/y2022/control_loops/superstructure/superstructure_position.fbs
+++ b/y2022/control_loops/superstructure/superstructure_position.fbs
@@ -8,6 +8,7 @@
   // down.
   intake_front:frc971.PotAndAbsolutePosition (id: 1);
   intake_back:frc971.PotAndAbsolutePosition (id: 2);
+  // Zero is forwards; positive = counter-clockwise.
   turret:frc971.PotAndAbsolutePosition (id: 3);
 
   // Zero is straight and positive is open