Initializing a service at app startup

Is there documentation on how to get a particular Service to initialize when the app starts?
I believe it has to do with the App Component, but is there an example I could look at?

A service will be initialized by the first component that uses it. If it is referenced on a subset of pages or components, it will only be initialized when you visit the first one. If you really need it done at the very start, you can reference it in the app component.

oh, so just have a local copy of the App component (which I probably need to customize anyway, and include a reference/dependency to that Service, thanks!