docs: Adding file to support staging reference docs

  <!-- Added to Gerrit so we can stage reference docs directly from

       Android builds; this file should *not* be migrated to Piper -->

  <meta name="top_category" value="develop" />

  <meta name="subcategory" value="reference" />

  <meta name="book_path" value="{% if book_path %}{{ book_path }}{% else %}/reference/_book.yaml{% endif %}" />

  <meta name="project_path" value="/reference/_project.yaml" />

  <meta name="page_type" value="reference" />