[JOSS] Comparison to SimPy

This issue is created as part of a review at https://github.com/openjournals/joss-reviews/issues/8502 .

I am trying to look at this from the perspective of a user who is using SimPy and is considering to transition to your code.

I think this would be useful for them:

• a list of which SimPy functions are and are not implemented in Serializable-SimPy
• an example of a SimPy program and how it looks with Serializable-SimPy
• guidelines on how to rewrite their code so that they only use Serializable-SimPy, or how to use both packages together

Could you include this in the documentation?