Add comments to stem.py and globals.py so people can find all the torrc options

sbws sets its own timeouts, so it should tell tor not to use adaptive timeouts:

'LearnCircuitBuildTimeout': 0,  # Disable adaptive circuit timeouts.

This was implemented in 0.3.0: https://github.com/torproject/sbws/issues/146 https://github.com/torproject/sbws/pull/147

But reverted in 0.4.0 by mistake: https://github.com/torproject/sbws/issues/151