Document that NavigationAgent height offset is mostly a placebo

Document that NavigationAgent height offset is mostly a placebo.

doc/classes/NavigationAgent3D.xml

@@ -86,7 +86,7 @@
 	</methods>
 	<members>
 		<member name="agent_height_offset" type="float" setter="set_agent_height_offset" getter="get_agent_height_offset" default="0.0">
-			The agent height offset to match the navigation mesh height.
+			The NavigationAgent height offset is subtracted from the y-axis value of any vector path position for this NavigationAgent. The NavigationAgent height offset does not change or influence the navigation mesh or pathfinding query result. Additional navigation maps that use regions with navigation meshes that the developer baked with appropriate agent radius or height values are required to support different-sized agents.
 		</member>
 		<member name="avoidance_enabled" type="bool" setter="set_avoidance_enabled" getter="get_avoidance_enabled" default="false">
 			If [code]true[/code] the agent is registered for an RVO avoidance callback on the [NavigationServer3D]. When [method NavigationAgent3D.set_velocity] is used and the processing is completed a [code]safe_velocity[/code] Vector3 is received with a signal connection to [signal velocity_computed]. Avoidance processing with many registered agents has a significant performance cost and should only be enabled on agents that currently require it.