Add registration notice

We need to gather a bit of information about the students. In particular, we need email, matrikel number, dkrz number and if we should forward information to the IMPRS office.

I believe there's currently no single portal which would allow us to collect these information all together, and a LimeSurvey seems to be a bit easier than handing out a piece of paper, just to type it in afterwards.

requested review from @m300575

changed the description

approved this merge request

merged

mentioned in commit 785d8b99

mentioned in merge request !38 (merged)