Add CoLab example

[AleKit]

Include Kyle's CoLab SWIFTGalaxy demo Jupyter Notebook.
closes #10

• Add the .ipynb file into the examples/ directory as a"cleanly run" copy
• Link at the top of the notebook to the interactive version on CoLab
• Add a README.rst file to the examples/ directory
• Direct users to the example directory in general (it's newly added) and to this basic example specifically in a few places: the main README.rst of the repository, and maybe one or two places in the docs hosted on RTD (think about suitable location(s))
• Add automated testing of this notebook to the github checks with the nbmake package. Add nbmake to the optional_requirements.txt file