change some of the examples in the main body to mdoc credential format.

[OIDF-automation]

Imported from AB/Connect bitbucket: https://bitbucket.org/openid/connect/issues/1919

Original Reporter: KristinaYasuda

to make clear that the specification supports multiple credential formats.

based on the conversation in openid / connect / issues / #1915 - "Verifiable Credentials" causes people to believe OID4VC supports W3C VCs only — Bitbucket

[Sakurann]

would be great if you could use some of the 18013-7 examples.

[awoie]

Examples are here. Can create a PR.