Update SETUP.md

[sanchitmalhotra126]

Two quick updates to the setup guide based on a few issues I ran into doing a fresh setup on a new machine (M1 Macbook Pro).

Links

Testing story

Deployment strategy

Follow-up work

Privacy

Security

Caching

PR Checklist:

• Tests provide adequate coverage
• Privacy and Security impacts have been assessed
• Code is well-commented
• New features are translatable or updates will not break translations
• Relevant documentation has been added or updated
• User impact is well-understood and desirable
• Pull Request is labeled appropriately
• Follow-up work items (including potential tech debt) are tracked and linked

[Hamms]

This change makes sense to me, but it might be a good idea to also get a review from someone familiar with homebrew and other mac-specific details

[sureshc]

This seems to be the standard solution for macOS since macOS 10.14. Wonder why it hasn’t popped up before. We have some other special configuration setup options for macOS related to openssl.