Restore concept check reference documentation.

doc/src/boost.xml

@@ -38,6 +38,20 @@
   <part id="libraries">
     <title>The Boost C++ Libraries (BoostBook Subset)</title>
     <xi:include href="libraries.xinclude" xpointer="xpointer(/*/node())"/>
+
+    <library name="Concept Check" dirname="concept_check">
+      <libraryinfo>
+        <author>
+          <firstname>Jeremy</firstname>
+          <surname>Siek</surname>
+        </author>
+        <librarypurpose>Tools for generic programming</librarypurpose>
+        <librarycategory name="category:generic"/>
+        <librarycategory name="category:testing"/>
+      </libraryinfo>
+      <title>Boost.Concept_Check</title>
+      <xi:include href="../../libs/concept_check/doc/reference/concepts.xml"/>
+    </library>
   </part>
 
   <part id="tools">