Update NodeNorm Jupyter Notebook and write some Translator-specific documentation

[gaurav]

The Jupyter Notebook is at https://github.com/TranslatorSRI/NodeNormalization/blob/master/documentation/NodeNormalization.ipynb and is mostly correct, but some minor updates should be made.

It would also be useful to have Translator-specific documentation that tells Translator users what to do if a clique is split or a preferred label is incorrect or missing.