title: Add reStructuredText support for Juptyer notebooks
body: <p>I needed to view reStructuredText files in JupyterLab, and the best I found so far was <a href="https://github.com/jupyter/help/issues/241#issuecomment-455207852" rel="nofollow noreferrer">@akaihola's answer</a> to a related <a href="https://github.com/jupyter/help/issues/241" rel="nofollow noreferrer">issue on github</a>.</p>
  
  <p>I added a work around that would allow rendering the file without viewing the source, provided below.</p>