Docs: Mark `SVGTexture` as experimental

doc/classes/SVGTexture.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8" ?>
-<class name="SVGTexture" inherits="Texture2D" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../class.xsd">
+<class name="SVGTexture" inherits="Texture2D" experimental="" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../class.xsd">
 	<brief_description>
 		A scalable [Texture2D] based on an SVG image.
 	</brief_description>