Add howto for adding a "Complementary Collection"

[koppor]

I'd like to add https://www.kaggle.com/datasets to "Complementary Collections", but I don't know how to do it here. It seems, only datasets are included here.

[caesar0301]

Currently we don't have a way to feed the Complementary Collections as convenient as datasets. You can make a PR against the root template, with the last part: https://github.com/awesomedata/apd-core/blob/master/deploy/index.mako