Document all FOREACH loops.

src/NoteDisplay.h

@@ -56,6 +56,7 @@ enum HoldType
 	NUM_HoldType,
 	HoldType_Invalid
 };
+/** @brief Loop through each HoldType. */
 #define FOREACH_HoldType( i ) FOREACH_ENUM( HoldType, i )
 const RString &HoldTypeToString( HoldType ht );
 
@@ -66,6 +67,7 @@ enum ActiveType
 	NUM_ActiveType,
 	ActiveType_Invalid
 };
+/** @brief Loop through each ActiveType. */
 #define FOREACH_ActiveType( i ) FOREACH_ENUM( ActiveType, i )
 const RString &ActiveTypeToString( ActiveType at );