Make counter example use `HierarchicalMachine` explicitly to be more clear

[MicahLyle]

If you run it with the regular Machine (imported from transitions) you'll get this error:

In [14]: collector = Machine(states=states, transitions=transitions, initial='waiting')
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-14-cb0d383f0648> in <module>
----> 1 collector = Machine(states=states, transitions=transitions, initial='waiting')

~/.virtualenvs/jst/lib/python3.9/site-packages/transitions/core.py in __init__(self, model, states, initial, transitions, send_event, auto_transitions, ordered_transitions, ignore_invalid_triggers, before_state_change, after_state_change, name, queued, prepare_event, finalize_event, model_attribute, on_exception, **kwargs)
    577
    578         if states is not None:
--> 579             self.add_states(states)
    580
    581         if initial is not None:

~/.virtualenvs/jst/lib/python3.9/site-packages/transitions/core.py in add_states(self, states, on_enter, on_exit, ignore_invalid_triggers, **kwargs)
    806                 if 'ignore_invalid_triggers' not in state:
    807                     state['ignore_invalid_triggers'] = ignore
--> 808                 state = self._create_state(**state)
    809             self.states[state.name] = state
    810             for model in self.models:

~/.virtualenvs/jst/lib/python3.9/site-packages/transitions/core.py in _create_state(cls, *args, **kwargs)
    638     @classmethod
    639     def _create_state(cls, *args, **kwargs):
--> 640         return cls.state_cls(*args, **kwargs)
    641
    642     @property

TypeError: __init__() got an unexpected keyword argument 'children'

[aleneum]

Hello @MicahLyle,

I guess for comprehensibility's sake it is better to use the actual machine classes (e.g. LockedMachine or HierarchicalMachine) in examples instead of importing them as Machine. Thanks for the PR!

[coveralls]

Coverage remained the same at 98.773% when pulling 700e1c7c7897ac50913a26a9e8b0685254af27ae on MicahLyle:readme-counter-example-hierarchical-machine-more-clear into 203fa8fc898d916d87b71527301a4c1294858789 on pytransitions:master.