Make introduction informative.

Author: gkellogg

spec/index.html

@@ -134,11 +134,11 @@
   <section id="related" data-include="./common/related.html"></section>
 </section>
 
-<section id="sec-intro">
+<section id="sec-intro" class="informative">
   <h2>Introduction</h2>
   <p>This document defines TriG, a concrete syntax for RDF as defined in the
   RDF Concepts and Abstract Syntax document
-  [[!RDF12-CONCEPTS]]. TriG is an extension of
+  [[RDF12-CONCEPTS]]. TriG is an extension of
   Turtle [[RDF12-TURTLE]], extended
   to support representing a complete <a data-cite="RDF12-CONCEPTS#dfn-rdf-dataset">RDF dataset</a>.
 </section>