Give a bit more information about how Plane Guided works

plane/source/docs/guided-mode.rst

@@ -4,10 +4,18 @@
 GUIDED Mode
 ===========
 
-The GUIDED mode is used when you want the aircraft to fly to a specific
-point on the map without setting up a mission. Most ground control
+GUIDED mode is used when you want the aircraft to fly to a specific
+point on the map, or in specific direction (heading) without setting up a mission. 
+
+Most ground control
 stations support a "click to fly to" feature where you can click a point
-on the map and the aircraft will fly to that location then loiter.
+on the map and the aircraft will fly to that location then loiter. If an 
+altitude is requested, the aircraft will fly at the current altitude until
+it reaches the target location, then will loiter down or up to the requested
+altitude. 
+
+The guided mode heading feature isn't supported by Mission Planner or QGC, but can be
+requested via MavLINK commands or using Lua.
 
 The other major use for GUIDED mode is in :ref:`geo-fencing <geofencing>`.
 When the geo-fence is breached the aircraft will enter GUIDED mode, and