Draft: Verifiable Credentials docs

[jessiemongeon1]

Thank you for your contribution to the IC Developer Portal. Before submitting your Pull Request, please make sure that:

• [ ] You have updated the .github/CODEOWNERS file according to your changes.
• [ ] You have registered new documents to /sidebars.js if any.

[lmuntaner]

@kristoferlund thanks a lot for your feedback!