Adding a token should be more clear

[aj-codecov]

This is two pieces of feedback

1. We should have a screenshot of exactly what copying the token into GH should look like:
   
   Something like this (but with a dummy token, not my nonsense in this screenshot)
2. We should emphasize that this is a necessary step you can't skip - recent feedback from Steven Eubank: I just thought I'd do it later and couldn't successfully setup until it came back, I was trying to set it up as an env var, not a repo secret (this is avoided if we drive people to click the link - can we pull the link out better? make it a button?