Update README.md to include TZ in Docker

[michael-robbins]

Gday! Just a small tweak, discovered in my new setup when I hadn't set the TZ correctly!

Without it the:

now = datetime.datetime.now()

parameters = {
    "d": now.strftime("%Y%m%d"),
    "t": now.strftime("%H:%M")
}

Would all default to UTC and then publish like a difference of -11 hours to PVOutput resulting in some funny looking production charts :D