Add doc to create non-StandardState and how to add fields

[musslick]

• add documentation on how to do it

[younesStrittmatter]

We already have this:

https://github.com/AutoResearch/autora-core/blob/main/docs/cycle/Dynamically%20Extending%20and%20Altering%20the%20State.ipynb

just needs to be included. Why it is in the cycle-folder? No clue...

I'll change put it to the appropriate position and add it to the documentation