<!-- modelo - coloque no head do seu blog -->
<link rel="search" type="application/opensearchdescription+xml"
title="Nome de sua busca" href="enderecodoseuxml.xml" />
<!-- no meu caso ficou assim -->
<link rel="search" type="application/opensearchdescription+xml"
title="Nome de sua busca" href="http://gist.github.com/raw/538189/74cd420485f38e4eb6d12de6535ccc796b3e6db3/vivaotux.xml" />