Archive this repository

The source code for Pangeo.io is now in https://github.com/pangeo-data/pangeo.io. I think we should:

[ ] Update the pinned repository in the pangeo-data organization to pangeo.io from https://github.com/pangeo-data/pangeo
[ ] Either enable organization wide GitHub discussions or only use https://discourse.pangeo.io/c/meta/10, in place of "This repo's issue tracker also serves as a general-purpose discussion forum"
[ ] Add a Disclaimer to the readme about the website source code and general discussions location moving
[ ] Archive this repository

pangeo-data / pangeo