Convert the User Guide into a notebook

[mepcotterell]

Currently, the User Guide is provided in plain Markdown. However, as it contains examples of ScalaTion code and ScalaTion Kernel commands, it would be better to provide it as a Jupyter notebook instead. Users with access to a Jupyter installation with ScalaTion Kernel would be able to use the guide interactively. Additionally, users would still be able to view a rendered preview of the guide here on GitHub as a fallback.