Add details for key verifications

[kiranaddepalli]

In addition we need a source of verification: Self-asssessment, Thirdparty review

[rlin1]

We need to store the KeyProtectionLevel and the entity that asserted it to the public Key

[rlin1]

We might want to add those two fields to the DIDdoc

[rlin1]

@kiranaddepalli : Could you please add that field to the respective element?

[rlin1]

Let’s add an „inline Issue” to the spec in the section where we define those additional attributes. That issue should state that we still need to register the additional attributes appropriately according to https://w3c.github.io/did-spec-registries/#the-registration-process.

[rlin1]

Please still add those changes into our spec - don't wait for the registration process to complete.

[kiranaddepalli]

@rlin1 , this is addressed in #287

[kiranaddepalli]

Changed the "Issue" to a "Note".