What should be part of an Onboarding doc?

I just joined Target at a Principal level. My manager is spread very thin and wants me to take initiatives and has told me to start networking heavily in the first few weeks. My plan is to create an Onboarding doc and share it with my manager. I'm going to use this doc to manage expectations and use it to review together 3 months down the line. How can I structure this doc? What pieces of information are more relevant/vital for such a doc. Any pointers?