Add tutorial to explain how to create a network from scratch

[mathbagu]

• Do you want to request a feature or report a bug?
  Feature

• What is the current behavior?
  There is no tutorial to explain how to create a network from scratch. I think we can create a simple one based on the well known eurostag1-tutorial: we have the factory in the code, the XML in the resources and probably the schema of the network somewhere, so it doesn't require so much time.

We would have to create a second one (or a second chapter in this tutorial to create the same network in Node/Breaker topology). This issue is linked to #140

• If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem

• What is the expected behavior?

• What is the motivation / use case for changing the behavior?
  Answer to the answer of Zach: https://spectrum.chat/powsybl/questions/is-there-any-beginners-guides-on-how-to-use-powsybl~e254b24e-1bb7-4183-9baa-736fe7ccb6f4

• Please tell us about your environment:

  • PowSyBl Version: ...
  • OS Version: ...

• Other information (e.g. detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, eg. stackoverflow, spectrum, etc)

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