Add retention roller flatbuffers

Signed-off-by: Maxwell Henderson <mxwhenderson@gmail.com>
Change-Id: I810162b41d563bbafe9e82544f2301ac63b21a9e
diff --git a/y2024/control_loops/superstructure/superstructure_output.fbs b/y2024/control_loops/superstructure/superstructure_output.fbs
index a429976..ddfc5ac 100644
--- a/y2024/control_loops/superstructure/superstructure_output.fbs
+++ b/y2024/control_loops/superstructure/superstructure_output.fbs
@@ -25,6 +25,10 @@
     // Positive voltage is for climber up
     // Negative voltage is for climber down
     climber_voltage:double (id: 6);
+
+    // Voltage of the retention rollers
+    // Positive voltage will hold the game piece in the catapult.
+    retention_roller_voltage: double (id: 7);
 }
 
 root_type Output;