[css3-syntax] Add a note about how qualified rules are usually style rules.

Author: tabatkins

css3-syntax/Overview.html

@@ -2732,6 +2732,8 @@ <h2 id=parsing><span class=secno>5. </span> Parsing</h2>
 
    <dd> A qualified rule has a prelude consisting of a list of component
     values, and a value consisting of a list of at-rules or declarations.
+    <p class=note> Most qualified rules will be style rules, where the
+     prelude is a selector.
 
    <dt><dfn id=declaration>declaration</dfn>
 

css3-syntax/Overview.src.html

@@ -2247,6 +2247,10 @@ <h2>
 			a prelude consisting of a list of component values,
 			and a value consisting of a list of at-rules or declarations.
 
+			<p class='note'>
+				Most qualified rules will be style rules,
+				where the prelude is a selector.
+
 		<dt><dfn>declaration</dfn>
 		<dd>
 			A declaration has a name,