Missing content for nltk

[piermarcobarbe]

Since nltk needs some data to be downloaded before being used, the notebook LDA-BBC will stop, requiring the user to download the needed data.
This can be done with:
from nltk import download
download('punkt')
download('averaged_perceptron_tagger')
download('wordnet')
download('stopwords')

It may be good to include these lines before running the notebook.