keep src/Doc;

--- a/Admin/Release/build_library	Sat Jan 16 15:57:38 2016 +0100
+++ b/Admin/Release/build_library	Sat Jan 16 16:37:45 2016 +0100
@@ -77,8 +77,6 @@
 
 echo "ISABELLE_FULL_TEST=true" >> etc/settings
 
-echo -n > src/Doc/ROOT
-
 env ISABELLE_IDENTIFIER="${ISABELLE_NAME}-build" \
   ./bin/isabelle build $JOBS -s -c -a -o browser_info \
     -o "document=pdf" -o "document_variants=document:outline=/proof,/ML"

--- a/lib/html/library_index_content.template	Sat Jan 16 15:57:38 2016 +0100
+++ b/lib/html/library_index_content.template	Sat Jan 16 16:37:45 2016 +0100
@@ -45,7 +45,8 @@
         is an extensional version of Martin-L&ouml;f's Type Theory.</li>
 
         <li><a href="Cube/index.html">Cube (The Lambda Cube)</a></li>
+
+        <li><a href="Doc/index.html">Sources of Documentation</a></li>
       </ul>
     </li>
   </ul>
-