Update documetation

[e1ee1e11]

There are four changes :

1. containers.rst:
   Add a newline to ensure syntax of admonition will take effect.
2. image.rst:
   a) The default value of wait argument in create() is True. (refs image.py#L101)
   b) The first argument in create() is the binary data of the image. Therefore, image_data should be opened in 'rb' mode. Or you will get an error like:

>>> image_data = open('an_image.tar.gz').read()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.4/codecs.py", line 319, in decode
    (result, consumed) = self._buffer_decode(data, self.errors, final)
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xfd in position 0: invalid start byte

3. operations.rst:
   Correct typo.

[codecov-io]

Codecov Report

Merging #314 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #314   +/-   ##
=======================================
  Coverage   96.31%   96.31%           
=======================================
  Files          11       11           
  Lines         814      814           
  Branches      100      100           
=======================================
  Hits          784      784           
  Misses         10       10           
  Partials       20       20

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[ajkavanagh]

Thanks very much for the corrections. Much appreciated!