a few quick notes that come to mind. As the commenters point out:
- DSGVO is indeed the German equivalent name to the GDPR (English term)
- "Imprint" isn't a privacy related topic that much, as such it's not really changed by the upcoming GDPR
- The GDPR changes many things, but the requirement for up front information isn't one of them - so it would've already been a rule to follow
Sometimes the question who is responsible for privacy information might not be that easy to decide when you're on platforms. I take this situation as being pretty clear though. You are basically given a blank slate, you can do with that page whatever you want, and the visitor has no clue whatsoever that it might be hosted by Github.
In addition to this, Github would be classified as a data processor (providing the tool) and you as the data controller who is in charge of practically everything except for the provision of the page.