dev: Document position target and attitude target support

Signed-off-by: Ryan Friedman <25047695+Ryanf55@users.noreply.github.com>

dev/source/docs/plane-commands-in-guided-mode.rst

@@ -10,6 +10,7 @@ This article lists the MAVLink commands that affect the movement of a Plane or Q
 
    The code which processes these commands can be found `here in GCS_Mavlink.cpp <https://github.com/ArduPilot/ardupilot/blob/master/ArduPlane/GCS_Mavlink.cpp>`__
 
+.. _movement_commands:
 Movement commands
 =================
 
@@ -55,3 +56,21 @@ These MAV_CMDs can be processed if packaged within a `COMMAND_INT <https://mavli
 - `MAV_CMD_GUIDED_CHANGE_SPEED <https://mavlink.io/en/messages/common.html#MAV_CMD_DO_CHANGE_SPEED>`__
 - `MAV_CMD_GUIDED_CHANGE_ALTITUDE <https://mavlink.io/en/messages/common.html#MAV_CMD_DO_CHANGE_ALTITUDE>`__
 - `MAV_CMD_GUIDED_CHANGE_HEADING <https://mavlink.io/en/messages/common.html#MAV_CMD_GUIDED_CHANGE_HEADING>`__
+
+Position Targets
+================
+
+To command the altitude in any supported frame, use `SET_POSITION_TARGET_GLOBAL_INT <https://mavlink.io/en/messages/common.html#SET_POSITION_TARGET_GLOBAL_INT>`__.
+Ensure to set the `POSITION_TARGET_TYPEMASK <https://mavlink.io/en/messages/common.html#POSITION_TARGET_TYPEMASK>`__ bit 3.
+
+To command the altitude in LOCAL frame, use `SET_POSITION_TARGET_LOCAL_NED <https://mavlink.io/en/messages/common.html#SET_POSITION_TARGET_LOCAL_NED>`__.
+It is currently not necessary to bother with `POSITION_TARGET_TYPEMASK <https://mavlink.io/en/messages/common.html#POSITION_TARGET_TYPEMASK>`__.
+The `MAV_FRAME <https://mavlink.io/en/messages/common.html#MAV_FRAME>`__ must be ``MAV_FRAME_LOCAL_OFFSET_NED``.
+
+No other fields in position target messages are currently supported. Use :ref:`movement_commands` to send a lat lon alt target.
+
+Attitude Targets
+================
+
+The low level attitude of the vehicle can be controlled with `SET_ATTITUDE_TARGET <https://mavlink.io/en/messages/common.html#SET_ATTITUDE_TARGET>`__.
+