Add CLI command to set/modify the module and site #72

Rather than instructing people to update their pyproject.toml to set the module and site, we should have a CLI command that sets it.

The CLI should prompt the user for both the module (python file) and site (the Site variable in the Python module) with default of app for both and then update the tool.render-engine.cli portion of the TOML file with the supplied values.