Add section on readme about how to remove/uninstall connector from the device

[smellai]

Add section on readme about how to remove/uninstall connector from the device

[rsora]

Actually we need to implement the uninstall functionality directly into the connector 😃
Anyway i.e. on a raspberry pi the following commands can be issued to clean completely the connector installation

 sudo systemctl stop ArduinoConnector.service
 sudo systemctl disable ArduinoConnector.service
 sudo rm /etc/systemd/system/ArduinoConnector.service
 sudo systemctl daemon-reload
 sudo systemctl reset-failed
 
 cd  <arduino-connector home folder>
 sudo rm -f arduino-connector.cfg certificate.key certificate.pem
 sudo rm -f arduino-connector
 sudo rm -rf sketches
 sudo rm -rf updates