[devhelp] docs: add index of new symbols in 3.28

[Sébastien Wilmet <swilmet src gnome org>]

commit c0cd7eee49aa729594fb9c4dad72aca5f9339554
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Sun Dec 3 13:27:20 2017 +0100

    docs: add index of new symbols in 3.28

 docs/reference/devhelp-docs.xml |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/docs/reference/devhelp-docs.xml b/docs/reference/devhelp-docs.xml
index 1532bb0..ae3647d 100644
--- a/docs/reference/devhelp-docs.xml
+++ b/docs/reference/devhelp-docs.xml
@@ -68,5 +68,9 @@
       <title>Index of new symbols in 3.26</title>
       <xi:include href="xml/api-index-3.26.xml"><xi:fallback /></xi:include>
     </index>
+    <index id="api-index-3-28" role="3.28">
+      <title>Index of new symbols in 3.28</title>
+      <xi:include href="xml/api-index-3.28.xml"><xi:fallback /></xi:include>
+    </index>
   </part>
 </book>