Added searchbox to documentation.

This provides the entry point of the documentation search feature.

Change-Id: Iea2b707995c0e042829db509927384dcec7aaf43
diff --git a/Documentation/config-labels.txt b/Documentation/config-labels.txt
index c08d484..ba3d482 100644
--- a/Documentation/config-labels.txt
+++ b/Documentation/config-labels.txt
@@ -315,3 +315,6 @@
 GERRIT
 ------
 Part of link:index.html[Gerrit Code Review]
+
+SEARCHBOX
+---------