Updating getfedora.org with atlas.hashicorp information

[Lalatendu Mohanty]

I think we should update the getfedora cloud pages [1] [2] with 
information about Fedora cloud base and atomic images are available at 
atlas [3] [4] as alternate download methods.

If we can't do the above, some information about having the boxes in 
atlas [4] in getfedora/cloud would help. So that users who likes to 
fetch the boxes from atlas.hashicorp will move in that direction.

[1] https://getfedora.org/en/cloud/download/index.html
[2] https://getfedora.org/en/cloud/download/atomic.html
[3] https://fedoramagazine.org/fedora-cloud-vagrant-boxes-atlas/
[4] https://atlas.hashicorp.com/fedora

-Lala