Add documentation for the Index library to clang's web page.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@75222 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/InternalsManual.html b/docs/InternalsManual.html
index a4d5a05..2e825c6 100644
--- a/docs/InternalsManual.html
+++ b/docs/InternalsManual.html
@@ -67,6 +67,7 @@
   <li><a href="#Constants">Constant Folding in the Clang AST</a></li>
   </ul>
 </li>
+<li><a href="libIndex.html">The Index Library</a></li>
 </ul>