[spec] Add additional examples

[timcappalli]

trafficstars

The examples section currently only has government ID and some TBD text.

    <p id="credential-type-examples">
      There are many types of digital credential that can be conveyed using
      this API. <dfn data-lt="credential type examples">Examples of these
      types</dfn> include:
    </p>
    <ul>
      <li>a driver's license or identity card issued by a government
      institution
      </li>
      <li>TBW: other credential types
      </li>
    </ul>

Update to include:

• employee ID
• federated sign in
• verified claim (phone, email)