feat: starting to flesh out initial spec-text

[bcoe]

This is mainly meant to get the conversation started, _what do we think the appropriate level of granularity is for describing a new method that relies on external RFCs/algorithms?

• Should we define in detail the steps involved in populating a typed array with random values, WebCrypto leaves it to: "Overwrite all elements of array with cryptographically random values of the appropriate type".
• In what amount of detail should we define the UUID V4 algorithm in spec-text?

CC: @syg, this might be an interesting topic of conversation for the Standard Library Task Group, if folks are supportive of its formation.

[littledan]

It looks like this PR was produced by starting from the rendered JS spec. I'd recommend starting from the source, which you can then build with ecmarkup. This will be a friendlier syntax!