Clarify the behavior of `RigidBody.CENTER_OF_MASS_MODE_AUTO`

doc/classes/RigidBody2D.xml

@@ -140,7 +140,7 @@
 		</member>
 		<member name="center_of_mass" type="Vector2" setter="set_center_of_mass" getter="get_center_of_mass" default="Vector2(0, 0)">
 			The body's custom center of mass, relative to the body's origin position, when [member center_of_mass_mode] is set to [constant CENTER_OF_MASS_MODE_CUSTOM]. This is the balanced point of the body, where applied forces only cause linear acceleration. Applying forces outside of the center of mass causes angular acceleration.
-			When [member center_of_mass_mode] is set to [constant CENTER_OF_MASS_MODE_AUTO] (default value), the center of mass is automatically computed.
+			When [member center_of_mass_mode] is set to [constant CENTER_OF_MASS_MODE_AUTO] (default value), the center of mass is automatically determined, but this does not update the value of [member center_of_mass].
 		</member>
 		<member name="center_of_mass_mode" type="int" setter="set_center_of_mass_mode" getter="get_center_of_mass_mode" enum="RigidBody2D.CenterOfMassMode" default="0">
 			Defines the way the body's center of mass is set.

doc/classes/RigidBody3D.xml

@@ -146,7 +146,7 @@
 		</member>
 		<member name="center_of_mass" type="Vector3" setter="set_center_of_mass" getter="get_center_of_mass" default="Vector3(0, 0, 0)">
 			The body's custom center of mass, relative to the body's origin position, when [member center_of_mass_mode] is set to [constant CENTER_OF_MASS_MODE_CUSTOM]. This is the balanced point of the body, where applied forces only cause linear acceleration. Applying forces outside of the center of mass causes angular acceleration.
-			When [member center_of_mass_mode] is set to [constant CENTER_OF_MASS_MODE_AUTO] (default value), the center of mass is automatically computed.
+			When [member center_of_mass_mode] is set to [constant CENTER_OF_MASS_MODE_AUTO] (default value), the center of mass is automatically determined, but this does not update the value of [member center_of_mass].
 		</member>
 		<member name="center_of_mass_mode" type="int" setter="set_center_of_mass_mode" getter="get_center_of_mass_mode" enum="RigidBody3D.CenterOfMassMode" default="0">
 			Defines the way the body's center of mass is set.