[README] Add instructions for creating xcodeproj

[kaydeearts]

Description

Adding this so that we have clear instructions on how to create xcodeproj for debugging & development.
Do we need more detail?

Checklist:

• I have followed the Contribution Guidelines
• I have added test code and data to prove that my code functions correctly
• I have verified that new and existing tests pass locally with my changes
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation

[josh-hadley]

thank you 😸