Update instructions on building and viewing docs

[sbellem]

The current docs at https://initc3.github.io/HoneyBadgerMPC/latest/development/getting-started.html#building-and-viewing-the-documentation are inaccurate.

Use the Makefile to provide targets to build and view the docs as in:

docs: ## generate Sphinx HTML documentation
    docker-compose -f docs.yml run --rm builddocs make -C docs clean
    docker-compose -f docs.yml up builddocs
    docker-compose -f docs.yml stop viewdocs
    docker-compose -f docs.yml up -d viewdocs

servedocs: docs ## compile the docs watching for changes
    docker-compose -f docs.yml stop viewdocs
    docker-compose -f docs.yml up -d viewdocs
    $(BROWSER) index.html

[sbellem]

Addressed in #449.