Documentation improvements

[IgnacioJPickering]

The following would improve the bblean docs:

• Usable "user guide" with jupyter notebooks (using nbsphinx probably) right now it is a placeholder
• Document the CLI
• Improve all docstrings and use a docstring style consistently throughout
• Deploy a "stable" version of the docs to gh pages, on published releases
• Fix issue with SCM version not being correctly added to the docs
• add min python version
• add swap info on linux

[kzsigmond]

@IgnacioJPickering Adding the minimum Python version to the installation instructions could be helpful.