Documentation should give a hint with defining diskette configuration with model using m2m

[sveetch]

Is your feature request related to a problem? Please describe.

It is currently not clear about m2m transitions tables if they are to be defined in configuration or not.

The command diskette_apps output will include the transitions tables in the model list.

Although it is documented in Django fixtures documentation, it is not clearly exposed in Diskette doc.

Describe the solution you'd like

Commonly those transition tables should be included in model list but we need to ensure there is no possible problems with it in specific context, we should ensure about this and possibly add a tip about it if needed.

Describe alternatives you've considered

Currently, developer have to know how Django fixtures work in practice and should refer to Django documentation to properly know how to define model list. So this is not a breaking issue but it would be nice to make it clear.