added some arvr docs

doc/classes/ARVRAnchor.xml

@@ -60,6 +60,7 @@
 	</methods>
 	<members>
 		<member name="anchor_id" type="int" setter="set_anchor_id" getter="get_anchor_id">
+			The anchor's id. You can set this before the anchor itself exists. The first anchor gets an id of [code]1[/code], the second an id of [code]2[/code], etc. When anchors get removed, the engine can then assign the corresponding id to new anchors. The most common situation where anchors 'disappear' is when the AR server identifies that two anchors represent different parts of the same plane and merges them.
 		</member>
 	</members>
 	<constants>

doc/classes/ARVRController.xml

@@ -31,6 +31,7 @@
 			<return type="int" enum="ARVRPositionalTracker.TrackerHand">
 			</return>
 			<description>
+				Returns the hand holding this controller, if known. See TRACKER_* constants in [ARVRPositionalTracker].
 			</description>
 		</method>
 		<method name="get_is_active" qualifiers="const">
@@ -77,6 +78,7 @@
 	</methods>
 	<members>
 		<member name="controller_id" type="int" setter="set_controller_id" getter="get_controller_id">
+			The controller's id. The first controller that the [ARVRServer] detects will have id 1, the second id 2, the third id 3, etc. When a controller is turned off, it's slot is freed. This ensures controllers will keep the same id even when controllers with lower ids are turned off.
 		</member>
 	</members>
 	<signals>

doc/classes/ARVROrigin.xml

@@ -35,6 +35,8 @@
 	</methods>
 	<members>
 		<member name="world_scale" type="float" setter="set_world_scale" getter="get_world_scale">
+			Allows you to adjust the scale to your game's units. Most AR/VR platforms assume a scale of 1 game world unit = 1 meter in the real world.
+			Note that this method is a passthrough to the [ARVRServer] itself.
 		</member>
 	</members>
 	<constants>

doc/classes/ARVRPositionalTracker.xml

@@ -17,6 +17,7 @@
 			<return type="int" enum="ARVRPositionalTracker.TrackerHand">
 			</return>
 			<description>
+				Returns the hand holding this tracker, if known. See TRACKER_* constants.
 			</description>
 		</method>
 		<method name="get_joy_id" qualifiers="const">
@@ -80,10 +81,13 @@
 	</methods>
 	<constants>
 		<constant name="TRACKER_HAND_UNKNOWN" value="0">
+			The hand this tracker is held in is unknown or not applicable.
 		</constant>
 		<constant name="TRACKER_LEFT_HAND" value="1">
+			This tracker is the left hand controller.
 		</constant>
 		<constant name="TRACKER_RIGHT_HAND" value="2">
+			This tracker is the right hand controller.
 		</constant>
 	</constants>
 </class>

doc/classes/ARVRServer.xml

@@ -121,6 +121,7 @@
 	</methods>
 	<members>
 		<member name="world_scale" type="float" setter="set_world_scale" getter="get_world_scale">
+			Allows you to adjust the scale to your game's units. Most AR/VR platforms assume a scale of 1 game world unit = 1 meter in the real world.
 		</member>
 	</members>
 	<signals>