Fix note about learn.h2o.ai, point to DNN FAQ and update the FAQ to include python

Description

I saw in the log helpful advices unfortunately with url that doesn't exist anymore.
Such as:
```
WARN water.default: *) Run h2o.interaction(...,pairwise=F) on high-cardinality categorical columns to limit the factor count, see http://learn.h2o.ai
```

Fixed

Assignee

Tomas Fryda

Fix versions

Reporter

Tomas Fryda

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Major