title: how to set include directory for rebar
body: <p>In my module I have</p>
  
  <pre><code>-include("blah.hrl").
  </code></pre>
  
  <p>The <code>.hrl</code> file is not in the module's directory, but somewhere else on my system. How can I make <code>rebar</code> find it when compiling? Is there a way to add a path to the include directory in <code>rebar.config</code>?</p>