Add spec up spec

[decentralgabe]

Fix #131

This is the first step in making web5 spec more formal, yay!

Next steps:

• Make sure there is clear normative language (MUST, MUST NOT, etc) around features that we want implemented and tested
• Open issues for all the TODOs in the spec & add more TODOs
• Make sure all features are covered in the spec, and see if there are sections we can refine or remove (like that around key management)
• Consider whether we want to add anything around the API to the spec (cc: @KendallWeihe @frankhinek)
• Remove the README and generate a GH pages doc...then cut a first version we can publish

Separately, once we agree on the language in the spec and the features we can create a related spec for conformance testing. Here we can note the features, the associated test vectors, and whether the implementations we have are conformant against them.

Open to any & all feedback.

[decentralgabe]

It might be easiest for you to review this if you check out the branch and render the spec yourself.

You can do that with ...

git fetch
git checkout origin/spec-up
cd spec
npm i
npm run build
open build/index.html

[decentralgabe]

@KendallWeihe @nitro-neal @frankhinek @mistermoe I have incorporated all feedback. I'd like to get this merged and publishing as-is.

Then I will work on a follow up PR for aligning normative statements (MUSTs) to test vectors we have, in addition to removing the README and GH-pageifying the spec.

[decentralgabe]

thanks @nitro-neal I added links to that section of the spec and an issue marker for #134