Add documentation

[wojas]

Writing documentation using mkdocs.

To view them locally from a checkout of the repo:

python3 -m venv .venv
.venv/bin/pip install -r docs/requirements.txt
.venv/bin/mkdocs serve

[neilcook]

.venv/bin/pip install -r requirements.txt

Should be:

.venv/bin/pip install -r docs/requirements.txt

Or mkdocs.yml needs to be in the docs directory.

[wojas]

Should be: .venv/bin/pip install -r docs/requirements.txt

Thanks, updated.

Or mkdocs.yml needs to be in the docs directory.

MkDocs is picky about it not being in the docs directory, unfortunately.