doc: obs_seq is being used as the module import and the object name in the docs.

[hkershaw-brown]

Bad docs, the example has the instance of the class overides the module name

>>> from pydartdiags.obs_sequence import obs_sequence as obs_seq
>>> obs_seq = obs_seq.obs_sequence('/Users/hkershaw/DART/Bugs/DuplicateObs/NCEP+ACARS.201303_6H.obs_seq2013030306')
>>> obs_seq = obs_seq.obs_sequence('/Users/hkershaw/DART/Bugs/DuplicateObs/obs_seq.0Z.20160421')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'obs_sequence' object has no attribute 'obs_sequence'
>>> type(obs_seq)
<class 'pydartdiags.obs_sequence.obs_sequence.obs_sequence'>

vs.

>>> from pydartdiags.obs_sequence import obs_sequence as obsq
>>> obs_seq = obsq.obs_sequence('/Users/hkershaw/DART/Bugs/DuplicateObs/obs_seq.0Z.20160421')
>>> obs_seq = obsq.obs_sequence('/Users/hkershaw/DART/Bugs/DuplicateObs/NCEP+ACARS.201303_6H.obs_seq2013030306')
>>> type (obs_seq)
<class 'pydartdiags.obs_sequence.obs_sequence.obs_sequence'>
>>> type (obsq)
<class 'module'>

readme.md