title: How to point to custom stubs directory in mypy via MYPY environment variable or mypy_path variable
body: <p>I have created a stub file and put it along side of the original file as suggested. However I get <code>missing library stubs or py.typed marker</code> error. I tried adding the stubs directory using <code>mypy_path</code> variable in my config file. Still getting the same error. Any suggestions?
  This is how I am initiating mypy:</p>
  <pre><code> mypy --namespace-packages  --explicit-package-bases --config-file &lt;setup.cfg&gt; &lt;mypy_file_to_typehint&gt;
  </code></pre>
  <p>My setup.cfg has the following:</p>
  <pre><code>[mypy]
  mypy_path = &lt;directory path&gt;
  </code></pre>