title: mypypath: Cannot find module named 'tzwhere'
body: <p>I am learning mypy, and the first error I got is <code>cannot find module</code>.</p>
  
  <p>My file is:</p>
  
  <pre><code>from tzwhere import tzwhere
  tzw = tzwhere.tzwhere()
  print(tzw)
  </code></pre>
  
  <p>It is runnable by python because <code>tzwhere</code> package is installed. But when I run it through mypy I get this:</p>
  
  <pre><code>mypy mp.py
  mp.py:1: error: Cannot find module named 'tzwhere'
  mp.py:1: note: (Perhaps setting MYPYPATH or using the "--ignore-missing-imports" flag would help)
  </code></pre>
  
  <p>How do I make it say <code>No library stub file for module 'tzwhere'</code> and deal with stub files instead of <code>Cannot find module</code>?</p>