Notes on improving the documentation

[jodemaey]

• There was a confusion with the problems created by Python 3.14 multiprocessing switching its default start method for processes. This need to be removed (or modified):

[jodemaey]

• A comment on the guarding of mutliprocessed Python 3.14 main script should be added somewhere and examples must be modified to include this guarding.

[jodemaey]

• The signature of the functions returning the tendencies and the Jacobian should be documented (in an info box).