Adds Sphinx documentation

[heyhaleema]

This PR:

• Adds Sphinx documentation (to be later published to Read The Docs)
• Adds Sphinx and the Read The Docs Sphinx theme installations to requirements.txt
• Resolves #7

To generate HTML-based documents documents:

• Install Sphinx, i.e. run pip install sphinx or re-run pip install -r requirements.txt
• Install Read The Docs Sphinx theme, i.e. run pip install sphinx-rtd-theme or re-run pip install -r requirements.txt
• Run make html from the docs folder

To view, open index.html in your web browser.

I will raise a new issue for the clean up/further enhancement documentation (e.g. review our docstrings based on this guidance).