title: Find matching partial string
body: <p>I can't seem to find an answer on google, nor the mongoose website, so I am asking here. If it is possible, how can I search for a partially matching string in a document.</p>
  
  <p>ex: </p>
  
  <p>In a user collection:</p>
  
  <pre><code>{ name: "Louis", location: "Paris, France" },
  { name: "Bill", location: "Paris, Illinoid" },
  { name: "Stephen", location: "Toronto, Ontario" }
  </code></pre>
  
  <p>mongoose function:</p>
  
  <pre><code>searchForCity("Paris");
  </code></pre>
  
  <p>The result would be a list of documents from the User collection having "Paris" in the location String. ex:</p>
  
  <pre><code>[
      { name: "Louis", location: "Paris, France" },
      { name: "Homer", location: "Paris, Illinois" }
  ]
  </code></pre>