Add logo to the README page

[JanBenisek]

We would like logo on the README page.
Tobania marketing can help here.

[sborms]

Update: Tobania is informed and said they would deliver a logo by end of March.

Reminder to myself: put the video of Jan's DS meetup talk somewhere visible (https://www.youtube.com/watch?v=w7ceZZqMEaA&feature=youtu.be).