Update fleet-on-ubuntu.md (#1825)
Update fleet-on-ubuntu.md (#1825)

- Updat binary names to reflect binaries in latest archive
- Add line to 'sudo cp fleet/linux/fleetctl  /usr/bin/fleetctl
- Change echo string for enroll_secret to use sudo tee due to permission denied
kolide/kolide,kolide/kolide,kolide/kolide,kolide/kolide