Adding a Github source requires you to authenticate with Github. When doing so, Github will ask if you want to add the Savannah app to your Github organizations, but this is not necessary. Once you have authenticated with Github, Savannah will ask you which of the organizations you are a member of you want to use.
If you are not a member of the organization you want to track in Savannah, but it is a public organization in Github, you can still track it by using the
other... option and providing the full URL to the Github organization.
Any public repository under your Github organization will be available to track as a Channel in Savannah.