sneaking the UFZ logo into the readme

As assumed in #384 (closed) by @schaefed - adding a logo among the UFZ and RDM logos gives a colorful logo salad. Organizing them as @schueler suggestests might need some more advanced html-container juggling that i am not quite capable of.

I managed to sneak it in as paragraph icon to the Major heading, which looks reasonably natural i find and also aligns well in normal screen scaling. You might have a look.