Need for tutorial about creation of propulsion models

[christophe-david]

Propulsion models are managed differently than other disciplines in FAST-OAD and, as @younes-jc suggested to me, a tutorial notebook to explain how to create propulsion models for FAST-OAD would be useful.

[christophe-david]

It is planned to modify the performance module so that propulsion models can be vanilla OpenMDAO components. Though this may take some time, the mentioned tutorial is thus bound to become obsolete. The effort to produce it has to be taken in consideration...