Tweak SkeletonModifier3D document for _process_modification_with_delta

doc/classes/SkeletonModifier3D.xml

@@ -26,6 +26,7 @@
 				Override this virtual method to implement a custom skeleton modifier. You should do things like get the [Skeleton3D]'s current pose and apply the pose here.
 				[method _process_modification_with_delta] must not apply [member influence] to bone poses because the [Skeleton3D] automatically applies influence to all bone poses set by the modifier.
 				[param delta] is passed from parent [Skeleton3D]. See also [method Skeleton3D.advance].
+				[b]Note:[/b] This method may be called outside [method Node._process] and [method Node._physics_process] with [param delta] is [code]0.0[/code], since the modification should be processed immediately after initialization of the [Skeleton3D].
 			</description>
 		</method>
 		<method name="_skeleton_changed" qualifiers="virtual">