fix: added example using eddsa_to_pub to documentation

[Andy53]

Description

Added an example to the documentation demonstrating eddsa_to_pub function.

Problem*

Function was not currently documented.

Resolves [https://github.com//issues/4574]
closes #4574

Summary*

Added documentation for eddsa_to_pub function.

Documentation*

Check one:

• No documentation needed.
• Documentation included in this PR.
• [Exceptional Case] Documentation to be submitted in a separate PR.

PR Checklist*

• [ X] I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[github-actions]

Thank you for your contribution to the Noir language.

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