Add systemd service file for caddy
Add some README with basic setup instructions
Explain how to view the service configuration
Add a note about permissions
Add a comment about run user and group
service->service unit
A systemd service can consist of different units. A unit configuration
file has the `.service` file ending which is a bit confusing, so please
be considerate if I'm confusing `service` and `unit` in the README
Fix typos/reword
Add contact information
