title: what does it mean to use DEFINE_string
body: <pre><code>DEFINE_string(
      calculator_graph_config_file, &quot;&quot;,
      &quot;Name of file containing text format CalculatorGraphConfig proto.&quot;);
  </code></pre>
  <p>This is part of a code offered by Google's mediapipe for image recognition can someone tell me what this (DEFINE_string) does?</p>