fold change results can be confusing

[zakandrewking]

If the data changes sign, then the fold and log(fold) say (nd). Explain this in the docs.

Also, python docs can be improved:

• Annoying, and confusing, to jump back to JavaScript docs for kwargs definitions
• Need an example for comparison data
• Putting docs in example notebooks is not ideal. Get the Python stuff into readthedocs.

[zakandrewking]

• add Python package info to the homepage