"This is a boolean value, and is False by default."

Not true; the next sentence in the description explains where the 
default value comes from.

I'd join both paragraphs to make it more clear:

"""A boolean value indicating whether this thread is a daemon thread 
(True) or not (False). This must be set before start() is called, 
otherwise RuntimeError is raised. Its initial value is inherited from 
the creating thread; the main thread is not a daemon thread.

The entire Python program exits ..."""