Add did:unitrust method

[zengmenglu]

DID Method Registration

As a DID method registrant, I have ensured that my DID method registration complies with the following statements:

• The DID Method specification defines the DID Method Syntax.
• The DID Method specification defines the Create, Read, Update, and Deactivate DID Method Operations.
• The DID Method specification contains a Security Considerations section.
• The DID Method specification contains a Privacy Considerations section.
• The JSON file I am submitting has passed all automated validation tests below.
• The JSON file contains a contactEmail address [OPTIONAL].
• The JSON file contains a verifiableDataRegistry entry [OPTIONAL].

[msporny]

Meets minimum requirements for registration.

[gatemezing]

Meets minimum requirements for registration.