Added searchbox to documentation.

This provides the entry point of the documentation search feature.

Change-Id: Iea2b707995c0e042829db509927384dcec7aaf43
diff --git a/Documentation/error-multiple-changeid-lines.txt b/Documentation/error-multiple-changeid-lines.txt
index 9fa2b91..9b094d4 100644
--- a/Documentation/error-multiple-changeid-lines.txt
+++ b/Documentation/error-multiple-changeid-lines.txt
@@ -29,3 +29,6 @@
 GERRIT
 ------
 Part of link:error-messages.html[Gerrit Error Messages]
+
+SEARCHBOX
+---------