message: Add link to data extraction guide
diff: The API accepts GET and POST requests. POST methods use content type
  <code>application/json</code>
  </p>
  + <h3 id="Extraction">Data Extraction</h3>
  + <p>The Postcodes.io application and database are packaged as docker images for rapid local deployment and data extraction.</p>
  + <p>To perform one-time data extraction tasks using SQL, see our <a href="https://ideal-postcodes.co.uk/guides/postcodes-io-database">local data extraction guide</a>.</p>
  <h3 id="Responses">Responses</h3>
  <p>JSON(P) only. CORS is enabled.</p>
  <p>
  