Fix Sphinx documentation issues. about msticnb HOT 1 OPEN

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MsticpyImportExtraError - Error importing Scikit Learn and matplotlib
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Cannot use this feature without Sklearn and matplotlib installed
This feature requires one or more additional packages to be installed.
To do this run the command:
pip install msticpy[ml]

For more help on fixing this error see:
 - Installing msticpy

Exception context:
Stack:
  File "<frozen importlib._bootstrap_external>", line 728, in exec_module

  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed

  File "/home/docs/checkouts/readthedocs.org/user_builds/msticnb/envs/stable/lib/python3.7/site-packages/msticpy/analysis/eventcluster.py", line 56, in <module>
    extra="ml",

  File "/home/docs/checkouts/readthedocs.org/user_builds/msticnb/envs/stable/lib/python3.7/site-packages/msticpy/common/exceptions.py", line 436, in __init__
    super().__init__(*add_args, help_uri=uri, **kwargs)

  File "/home/docs/checkouts/readthedocs.org/user_builds/msticnb/envs/stable/lib/python3.7/site-packages/msticpy/common/exceptions.py", line 119, in __init__
    stack=traceback.format_stack(limit=5),

---
Locals:
self (MsticpyImportExtraError) = Cannot use this feature without Sklearn and matplotlib installed
help_uri (NoneType) = None
args (tuple) = ('Cannot use this feature without Sklearn and matplotlib installed',)
kwargs (dict) = {'title': 'Error importing Scikit Learn and matplotlib'}
extra (str) = ml
mssg (str) = This feature requires one or more additional packages to be installed.
To do this run the command:
pip install msticpy[ml]
add_args (list) = ['Cannot use this feature without Sklearn and matplotlib installed', 'This feature requires one or more additional packages to be installed.\nTo do this run the command:\npip install msticpy[ml]']
uri (tuple) = ('Installing msticpy', 'https://msticpy.readthedocs.io/en/latest/getting_started/Installing.html')
__class__ (type) = <class 'msticpy.common.exceptions.MsticpyImportExtraError'>
---
Exception was raised by:
Traceback (most recent call last):

  File "/home/docs/checkouts/readthedocs.org/user_builds/msticnb/envs/stable/lib/python3.7/site-packages/msticpy/analysis/eventcluster.py", line 48, in <module>
    from sklearn.cluster import DBSCAN

ModuleNotFoundError: No module named 'sklearn'

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