The SDK does cover the checklist commands quite well, this you can download in Developer Mode. I’d recommend you have a look at an existing checklist as an example.
Once created you place the new checklist in the community folder using the same path format (and file name) as the corresponding aircraft in the official folder. You could download one I have created and use this as an example:
https://www.flightsimhangar.co.uk/
@ScorpionFilm422 has created one for the Mooney: