:memo: Initialize documentation page

[weiji14]

Documentation built with Jupyter-Book/Sphinx. Deployed to GitHub Pages via GitHub Actions.

Preview at https://weiji14.github.io/zen3geo

TODO:

• [x] Add jupyter-book dev dependency
• [x] Initialize no-frills documentation built with Jupyter-Book
• [x] Setup GitHub Actions CI to build docs and push to GitHub Pages
• [ ] Use minimalistic theme (next time)

Note, need to update settings at https://github.com/weiji14/zen3geo/settings/pages

References:

• https://jupyterbook.org/en/stable/start/create.html
• https://jupyterbook.org/en/stable/publish/gh-pages.html#automatically-host-your-book-with-github-actions
• https://github.com/GenericMappingTools/egu22pygmt/pull/3