Explain delta signature scheme better

[dhh1128]

Moved from https://github.com/openssi/peer-did-method-spec/issues/126. Tagging @OR13 who opened it there.

[dhh1128]

@OR13 : The intent is to use JWS. However, when I first wrote the section, that wasn't the intent. So the current muddiness is probably the result of me claiming we're using JWS but not updating my verbiage everywhere. Sorry about the confusion.

[OR13]

Cool, IMO detached JWS is the best approach for these deltas, happy to help document that in the next version of the spec.

[OR13]

Here is the detached JWS delta I used for my implementation: https://raw.githubusercontent.com/transmute-industries/did-peer.js/master/packages/did-peer.js/src/fixtures/deltas/0.json

{
  "change": "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",
  "when": "2020-06-27T18:08:28.514Z",
  "by": [
    {
      "key": "#z6Mkf5rGMoatrSj1f4CyvuHBeXJELe9RPdzo2PKGNCKVtZxP",
      "sig": "eyJhbGciOiJFZERTQSIsImI2NCI6ZmFsc2UsImNyaXQiOlsiYjY0Il0sImtpZCI6ImRpZDprZXk6ejZNa2Y1ckdNb2F0clNqMWY0Q3l2dUhCZVhKRUxlOVJQZHpvMlBLR05DS1Z0WnhQI3o2TWtmNXJHTW9hdHJTajFmNEN5dnVIQmVYSkVMZTlSUGR6bzJQS0dOQ0tWdFp4UCJ9..zGzx3xHiN7fnejRKIvVgPUSgzzOZGs4MF5khGshaRLCRJgfD1lJpxuL0u5QZSE_Fidf5IT2pmFZwyYpHHz9wDw"
    }
  ]
}