Add Prerequisites to Readme

[nightguarder]

Motivation

Users need to know what prerequisites they need in order to run exo. Simple addition to docs prevents future raised issues.

Changes

Updated README.md:

• to include installation instructions for uv and macmon.

Updated CONTRIBUTING.md:

• to verify these prerequisites are met before starting development.

• Standardized on brew installation instructions for macOS users to keep the guide simple.

Why It Works

By listing these prerequisites upfront, users will set up their environment correctly before attempting to run exo.

Test Plan

Manual Testing

MacBook Pro M4

• Verified that uv and macmon were missing initially, causing failures
• after installing them via brew (as documented), uv run exo starts successfully.

Automated Testing

[Evanev7]

looks good, but I'd actually prefer people use the nix flake for development. I'm on the fence as it's a bit of a turn off for newcomers, but the readme changes definitely seem good.

[nightguarder]

Sorry Not familiar with nix. Will look into it. I just wanted to quickly get working on the project.

[Evanev7]

no worries! this is the exact problem I'm describing, it's not simple like brew so I think we probably should continue with brew in the CONTRIBUTING - and I think we should aim to support contributions from both dev environments as well