import non-API augur docs

[jameshadfield]

This is a progress-tracker type issue to track the incorporation of augur documentation into docs.nextstrain.org. The gdoc contains a mapping of how they map to the new docs TOC structure.

This does not include the API generated docs (i.e. https://docs.nextstrain.org/projects/augur/en/stable/api/api.html)

[eharkins]

This is done for now. See #17 to make sure submodule and/or subproject is in sync with this project. If #27 pans out, there will be some work again here to change implementation of including these docs.