Add library import example

[critesjosh]

Problem

Show the recommended way to import external libraries.

Proposed solution

Import this library and do a basic operation in an example circuit.

Alternatives considered

No response

Additional context

No response

Submission Checklist

• [ ] Once I hit submit, I will assign this issue to the Project Board with the appropriate tags.

[signorecello]

@critesjosh I think we could point lib imports to noir-examples 🙂 wdyt? would close this issue nevertheless

[critesjosh]

works for me!