add connection close reminders

[PixnBits]

For dummkopfs like myself who copy the example code, a reminder comment of the limitation/caveat to close the connection might be nice after all ;-) the installation steps (which driver? chip, db, etc.) that might go wrong and need debugging.

[PixnBits]

or would maybe a note of the possible process.on('exit', ...); would be more appropriate? (example)