Merge pull request #47108 from lawnjelly/software_skinning_docs

Add to 2d software skinning classref note about custom shaders

doc/classes/ProjectSettings.xml

@@ -1046,6 +1046,7 @@
 			If [code]true[/code], performs 2D skinning on the CPU rather than the GPU. This provides greater compatibility with a wide range of hardware, and also may be faster in some circumstances.
 			Currently only available when [member rendering/batching/options/use_batching] is active.
 			[b]Note:[/b] Antialiased software skinned polys are not supported, and will be rendered without antialiasing.
+			[b]Note:[/b] Custom shaders that use the [code]VERTEX[/code] built-in operate with [code]VERTEX[/code] position [i]after[/i] skinning, whereas with hardware skinning, [code]VERTEX[/code] is the position [i]before[/i] skinning.
 		</member>
 		<member name="rendering/2d/snapping/use_gpu_pixel_snap" type="bool" setter="" getter="" default="false">
 			If [code]true[/code], forces snapping of vertices to pixels in 2D rendering. May help in some pixel art styles.