[gtk+] docs: Add index for 3.18 api

[Rico Tzschichholz <ricotz src gnome org>]

commit 024a9c157319da63da1f537731204682487af5bb
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Tue Sep 15 07:30:36 2015 +0200

    docs: Add index for 3.18 api

 docs/reference/gdk/gdk-docs.sgml |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/docs/reference/gdk/gdk-docs.sgml b/docs/reference/gdk/gdk-docs.sgml
index 7831ede..bdd7a7a 100644
--- a/docs/reference/gdk/gdk-docs.sgml
+++ b/docs/reference/gdk/gdk-docs.sgml
@@ -97,6 +97,10 @@
     <title>Index of new symbols in 3.16</title>
     <xi:include href="xml/api-index-3.16.xml"><xi:fallback /></xi:include>
   </index>
+  <index id="api-index-3-18" role="3.18">
+    <title>Index of new symbols in 3.18</title>
+    <xi:include href="xml/api-index-3.18.xml"><xi:fallback /></xi:include>
+  </index>
 
   <xi:include href="xml/annotation-glossary.xml"><xi:fallback /></xi:include>