docs: add a note on setting environment variables in a CI environment

README.md

@@ -20,7 +20,8 @@ shipit
 In order to be able to authenticate with Github, you must set an environment
 variable called `GITHUB_TOKEN` to a
 [personal access token](https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/creating-a-personal-access-token)
-with `repo` permissions.
+with `repo` permissions. This must also be done when running in a CI
+environment.
 
 ## Granting permissions