Mark the "default stylesheets" section as being experimental.

Author: tabatkins

css-scoping-1/Overview.bs

@@ -51,6 +51,10 @@ Introduction</h2>
 <h2 id='default-element-styles'>
 Default Styles for Custom Elements</h2>
 
+	Advisement: This section is <strong>experimental</strong>,
+	and is under active discussion.
+	Do not implement without consulting the CSSWG.
+
 	When defining <a>custom elements</a>,
 	one often wants to set up "default" styles for them,
 	akin to the user-agent styles that apply to built-in elements.