Note that NavigationObstacles should only be used if necessary and for moving objects only

Note that NavigationObstacles should only be used if necessary and for moving objects only.

(cherry picked from commit d1959cabd9c9e3a7f1143d3ac7abdbff89eda5ed)

doc/classes/NavigationObstacle.xml

@@ -5,6 +5,7 @@
 	</brief_description>
 	<description>
 		3D obstacle used in navigation for collision avoidance. The obstacle needs navigation data to work correctly. This can be done by having the obstacle as a child of a [Navigation] node, or using [method set_navigation]. [NavigationObstacle] is physics safe.
+		[b]Note:[/b] Obstacles are intended as a last resort option for constantly moving objects that cannot be (re)baked to a navigation mesh efficiently.
 	</description>
 	<tutorials>
 	</tutorials>

doc/classes/NavigationObstacle2D.xml

@@ -5,6 +5,7 @@
 	</brief_description>
 	<description>
 		2D obstacle used in navigation for collision avoidance. The obstacle needs navigation data to work correctly. This can be done by having the obstacle as a child of a [Navigation2D] node, or using [method set_navigation]. [NavigationObstacle2D] is physics safe.
+		[b]Note:[/b] Obstacles are intended as a last resort option for constantly moving objects that cannot be (re)baked to a navigation mesh efficiently.
 	</description>
 	<tutorials>
 	</tutorials>