We currently have an interesting tutorial athttps://matplotlib.org/sampledoc/index.html. However, it is really old and wrong in places (matplotlib/sampledoc#26) and we think some of this should be in the main developer docs. The todo here is to maybe condense and move this sphinx how-to to the main developer documentation. Probably not too hard, but whoever does it should have some sphinx familiarity and check that it works.