Explain what Multi-addresses are, and how they relate to IPFS.

[Mr0grog]

At the Berlin developer summit, we decided multiaddresses or peer addresses were important to write a concept doc about.

We did not have time to write a rough draft, so we need to create a concept doc from scratch. Concept docs are concise, high-level descriptions of various core concepts in IPFS. They should strive to answer:

1. What is this?
2. How does it relate to the rest of IPFS?
3. How can (or should?) you use it? (Note: sometimes the answer is that you should understand it, but not use it. Bitswap is probably a good example.)
4. Where do you go to learn more?
5. What is the current state of affairs?

[johnnymatthews]

Can add content from:

• https://github.com/ipfs/ipfs-docs/issues/247
• https://multiformats.io/multiaddr/