Switch NSFW text from Python to Notebook format

[guibaq]

Changed NSFW_text.py to Jupyter Notebook format.

Indeed, the code reads like it was an extract from a Notebook; it doesn't read naturally in Python format (as it is currently), and it would be more readable to use a Notebook format instead.

In addition:

• added a sample data for the data df that seemed to be missing (bug fix). Just filled a few rows to give the idea, I understand that you don't want to share your training data
  

• added some doc to make the file more readable

Could not test the code because it relies on internal Twitter libraries.

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[spunsosig]

lgtm