DID Core Github changes

DID WG participants,

For your information, we have changed the default branch of the github
repository for the Decentralized Identifier Specification
<https://github.com/w3c/did-core> from *master* to *main*.

Some guidance for participants affected by this change is here
<https://github.com/w3c/did-core/issues/332#issuecomment-742053659>.

Please reach out to me if the provided guidance is not sufficient. I will
be happy to help.

-- 
Brent Zundel, DID WG co-Chair