Disable warnings for brightness

[wetnun]

unicorn-hat/library/UnicornHat/unicornhat.py

Line 236 in 657deff

if brightness < 30:

While yes, the HAT might not light up, unless I'm going to trap stdout for this, it's really annoying. There should be a flag to disable the warning (or env var, or whatever makes more sense) for when you know you're doing something that might not work.