Provide a Tutorial

[MSallermann]

It might be nice to provide a "step-by-step" tutorial (maybe as a separate repository, something like https://github.com/spirit-code/spirit-tutorial).
The overlap with our existing documentation should be kept minimal and the tutorial should be understood as a guide on where to start and what to look at in the documentation.
Overall this tutorial might be more digestible than being confronted with the whole documentation at once, and after completing the tutorial the user would then be familiar with the documentation and could use it to help himself.

This tutorial could include:

• A very short introduction to ASD. Maybe some references and our Hamiltonian.
• References to the parts of the documentation on how to compile etc.
• An explanation of the "Spirit workflow": Automate tasks with python scripts. Do post-processing and quick testing in the GUI. How to use the various outputs generated by Spirit. Ideally in the form of simple step-by-step guides.
• Easy and short example scripts for every method implemented in Spirit. Ideally these scripts would be close to a "real-world" application and would produce some tangible output (Might not be feasible). For example: Calculating the curie temperature of some material using the monte-carlo method. Or getting the energy-path for a skyrmion collapse using GNEB.
• Maybe some expample input files and how to model more complex materials (via e.g the pairs syntax)
• How to set up different geometries, like disks etc.

[GPMueller]

It would be important to have every version of the tutorial refer to a specific version of Spirit.

The tutorial should also include brief introductions to

• GNEB
• HTST
• MMF

and refer to the corresponding papers

Also, the question is in what form the tutorial should be hosted:

• GitHub Pages (as part of spirit-code.github.io)
• GitHub wiki
• readthedocs

[GPMueller]

It would be a good idea to provide a simple FAQ.md in the root folder, which could be linked to prominently in the Readme.
Questions I gather from issues #571, #573 and #604 include

• Which version of Spirit should I use?
• How can I retrieve the magnetization using Python?
• I installed the Python package. Where is the executable?
• What is p_state in the python scripts and why is it needed?
• What is the "active image" and why should I care?
• How can I configure a hexagonal or honeycomb lattice?
• How can I retrieve the magnetization when running the GUI?
• How can I create a chain of spin systems?
• What is Rx in the GNEB plot?
• How can I configure a certain spin configuration in the GUI? (-> mention "dragging" mode)
• How can I tell Spirit to use a different config-file?
• What is the meaning of <something> in the config-file?
• When do I need / when should I use the config-file?
• Where can I read up on the theoretical background? -> a few docs, the paper, theses