Further Improvements to Documentation

[rob-shalloo]

Just collating some next steps regarding the documentation:

• We should decide on the format for examples. A good idea from Ángel (who has implemented this on Wake-T) is to write the page, including python code and rst code into a .py file in a tutorial folder and then have sphinx autogenerate the page. An example is here: https://github.com/AngelFP/Wake-T/blob/master/tutorials/01_single_plasma_simulation.py with the rendering here https://wake-t.readthedocs.io/en/latest/tutorials/01_single_plasma_simulation.html#sphx-glr-tutorials-01-single-plasma-simulation-py
• It would be good to have a handful tutorials covering as broad a range of the code as possible. Perhaps if we can streamline/simplify the creation process then we can add more tutorials as good first issues
• The Overview of the Code section would be, I think, quite a nice place to elaborate on the reason for developing the code as well as some documentation relating to the standards adopted in the output files, representations of the pulse internal (similar to our recent z vs t representation discussion) etc etc. It would be nice if the basics were clear and easy to find without delving into the source code. We can also add a section on some general theory (perhaps for propagator or other). Also would be nice to have a list of codes (which can be updated continuously) which support lasy input

[RemiLehe]

Discussed offline with @MaxThevenet @AngelFP: we should add some documentation that describes these new features:
#139 #126