Adjust URL for learning materials

[dcwalk]

Currently the materials are active at:

• http://archivers.co
• https://datatogether.github.io/learning/

It doesn't look like adding a CNAME with archivers.co into gh-pages branch helps us maintain the /learning/ path... I'm not too sure but I think we fairly soon want to change where we serve content, and rethink the redirect structure

TODOs to mark as complete:

• Determine preferred URL (I am thinking like datatogether.org/learning?)
• Adjust how content is served
• Clean up existing redirect (cloudflare)
• Clean up existing content serving (GitHub pages)

[ebarry]

datatogether.org/learning looks great to me at least <3