message: Add screenshots to appdata (linux)
diff: <keyword>hours tracker</keyword>
  </keywords>
  <url type="homepage">https://toggl.com</url>
  - <!-- <screenshots> -->
  - <!-- <screenshot type="default">https://something.png</screenshot> -->
  - <!-- <screenshot>https://somethingelse.png</screenshot> -->
  - <!-- </screenshots> -->
  + <screenshots>
  + <screenshot type="default">https://toggl.github.io/toggldesktop/assets/images/linux_ui_main.png</screenshot>
  + <screenshot>https://toggl.github.io/toggldesktop/assets/images/linux_ui_edit.png</screenshot>
  + </screenshots>
  <update_contact>martin@toggl.com</update_contact>
  </application>
  