update config to match mkdocs 1.2.3

[higs4281]

Two minor config adjustments to comply with mkdocs version 1.2.3.

Testing

To test: install the docs_requirements.txt in your python env, build and serve the docs, and then check them at http://127.0.0.1:8000/

pip install -r docs_requirements.txt
mkdocs build
mkdocs serve

The first page of docs isn't linked to anywhere, but is there in case someone goes to the root at io.