Create decentralized data structures tutorial

[terichadbourne]

We'd like to create a beginner-friendly tutorial on decentralized data structures that would give some of the background needed before folks get to the "Basics" lessons.

This should include plain-English introductions to concepts such as:

• CID
• DAG

I'd love for folks with more experience to add their ideas to this issue so we can scope out what this intro should look like!

[mikeal]

Should also cover "what is a hash" and "what is content addressability"

[terichadbourne]

See PR #59 for the current lesson proposal from @mikeal