title: Total number of documents in pysolr
body: <p>How can I get the total number of documents matching the given query. I have use the query below:</p>
  
  <pre><code>result = solr.search('ad_id : 20')
  print(len(result))
  </code></pre>
  
  <p>Since the default returning value is '10', the output is only 10, but the count is 4000. How can I get the total number of counts?</p>