1. Put GOOGLE_API_KEY into main.go file.
2. Run make deploy to deploy the bin to Home Assistant.
3. Configure the integration in Home Assistant:

command_line:
  - sensor:
      name: Closest Pharmacy On-Duty
      unique_id: pharmacy_closest_on_duty
      icon: mdi:medication
      scan_interval: 21600 # Every 6 hours.
      command: >
        /config/packages/pharmacy/on-duty/bin \
          --lat={{ state_attr("zone.home", "latitude") }} \
          --lon={{ state_attr("zone.home", "longitude") }}
      value_template: >
        {% set pharmacy = value | from_json %}
        {{ pharmacy.distance }}
      json_attributes:
        - address
        - instructions
        - google_maps_link
        - phone
        - second_phone
      device_class: distance
      unit_of_measurement: km