Added poster via upload

[kudrixD]

I added a poster for the Comparing Credential Formats paper. It's the current draft of our work on a comparison matrix with lots of criteria to be evaluated. We feel it's a good basis to sparking a discussion and get us into further fleshing it out.

[elenachachkarova]

Hi @kudrixD, we accepted your poster but your format is a bit different to the rest, so if you want / have time, have a look at example one here and re-upload.