Setup and configure mkdocs, write initial docs

[NeilHanlon]

Description

We need a place to write documentation for PineSAM and accept contributions from non-technical end users who wish to add items to the FAQ, add information, and otherwise grow the project.

This is a fairly large PR but it is the result of about a week of work getting things setup and configured how we think it should be.

This change implements mkdocs and adds a bunch of content as well as a framework for additional documentation.

Related Issues

N/A

Screenshots

https://neil-forks.github.io/PineSAM-river/

Checklist

• [x] I have tested my changes locally and they work as expected.
• [x] I have updated the documentation, if applicable.
• [x] I have added appropriate tests, if applicable.
• [x] I have run the linter and fixed any issues, if applicable.

Other information

n/a

[River-Mochi]

the way you did the contributors at the bottom is my favorite part, clean and simple. black & white so it blends in unless you hover on names.