Add more detail to documentation

Signed-off-by: Caspar de Haes <caspar.dehaes@five.ai>

Author: caspar-ai

osi_trafficcommand.proto

@@ -487,11 +487,19 @@ message TrafficAction
         //
         optional ActionHeader action_header = 1;
 
-        // The custom command given to the traffic participant.
+        // The custom command given to the traffic participant.  Used to convey a specific instruction
+        // (for example "exit_highway"), or event (for example "left_indicator_activated").
+        //
+        // \note This corresponds to the content of the OpenSCENARIO 1.0 CustomCommandAction field.
         //
         optional string command = 2;
 
-        // The type of the custom command given to the traffic participant.
+        // The type of the custom command given to the traffic participant.  Can be used to simplify
+        // how commands are grouped, for example the command_type could be "sensor_failure" and the
+        // command value (above) could be "front_right_camera".  This prevents needing long commands
+        // (like "sensor_failure: front_right_camera").
+        //
+        // \note This corresponds to the "type" attribute of the OpenSCENARIO 1.0 CustomCommandAction.
         //
         optional string command_type = 3;
     }