Add automatic data preprocssing section to User Guide
I don't see a single place in the H2O User Guide where we talk about the automatic pre-processing that we do on the data prior to any machine learning. e.g. imputation, normalization, one-hot encoding, etc.
What we do differs for each algo, and it seems like some of the algo pages mention bits and pieces of this, but it would be nice to wrap this up into a small section on the Algorithms page: http://docs.h2o.ai/h2o/latest-stable/h2o-docs/data-science.html