Update index man page

Change-Id: Ia7042a61fd2e833ea90c3efd7c552552584f7cd7
Reviewed-on: http://review.couchbase.org/28770
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>