fmu-v5 manifest: Add some comments

Clarify which  componets is on which index for the item array

src/drivers/boards/px4fmu-v5/manifest.c

@@ -66,6 +66,9 @@ typedef px4_hw_mft_list_entry_t *px4_hw_mft_list_entry;
 
 static const px4_hw_mft_item_t device_unsupported = {0, 0, 0};
 
+// List of components on a specific board configuration
+// The index of those components is given by the enum (px4_hw_mft_item_id_t)
+// declared in board_common.h
 static const px4_hw_mft_item_t hw_mft_list_v0500[] = {
 	{
 		.present     = 1,