Added searchbox to documentation.

This provides the entry point of the documentation search feature.

Change-Id: Iea2b707995c0e042829db509927384dcec7aaf43
diff --git a/Documentation/dev-release-subproject.txt b/Documentation/dev-release-subproject.txt
index 956bd29..b9a39be 100644
--- a/Documentation/dev-release-subproject.txt
+++ b/Documentation/dev-release-subproject.txt
@@ -107,3 +107,6 @@
 GERRIT
 ------
 Part of link:index.html[Gerrit Code Review]
+
+SEARCHBOX
+---------