title: HTTPoison upload file
body: <p>is there any tutorial how to upload local files with HTTPoison.post ? 
  opening a file</p>
  
  <pre><code>{:ok, file} = File.open "README.md"
  HTTPoison.post("#{url}", file, headers)
  </code></pre>
  
  <p>this is for dropbox integration using upload functionality</p>
  
  <pre><code>curl -X POST https://content.dropboxapi.com/2/files/upload \
  --header "Authorization: Bearer " \
  --header "Dropbox-API-Arg: {\"path\":\"/Homework/math/Matrices.txt\",\"mode\": \"add\",\"autorename\": true,\"mute\": false}" \
  --header "Content-Type: application/octet-stream" \
  --data-binary @local_file.txt
  </code></pre>
  
  <p>the problem is how to send —data-binary file.</p>
  
  <p>Any ideas?</p>
  
  <p>Thanks</p>