docs: add Mac Intel (x86_64) CLI installation instructions

[shashax42]

Description

Added Mac Intel (x86_64) installation instructions alongside existing Apple Silicon support.

Changes

• Expanded Mac section to include both Intel and Apple Silicon architectures
• Added darwin-amd64 binary instructions for Intel Macs
• Kept existing darwin-arm64 instructions for Apple Silicon
• Clarified that Homebrew works for both architectures

Why this is needed

Mac Intel users currently only see "Mac (Apple Silicon)" instructions, which could lead to confusion about which binary to download.

Type of change

• Documentation update (non-breaking change which adds missing documentation)

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• The title of the PR states what changed and the related issues number (used for the release note).
• The title of the PR conforms to the Title of the PR
• I've included "Closes [ISSUE #]" or "Fixes [ISSUE #]" in the description (N/A - documentation improvement).
• I've updated both the CLI and UI to expose my feature (N/A - documentation only).
• Does this PR require documentation updates? (This IS a documentation update)
• I've updated documentation as required by this PR.
• I have signed off all my commits as required by DCO
• I have written unit and/or e2e tests for my change (N/A - documentation only).
• My build is green (troubleshooting builds).
• My new feature complies with the feature status guidelines (N/A - documentation only).
• I have added a brief description of why this PR is necessary and/or what this PR solves.
• Optional. My organization is added to USERS.md.
• Optional. For bug fixes, I've indicated what older releases this fix should be cherry-picked into (N/A - documentation can go to master only).

[bunnyshell]

🔴 Preview Environment stopped on Bunnyshell

See: Environment Details | Pipeline Logs

Available commands (reply to this comment):

• 🔵 /bns:start to start the environment
• 🚀 /bns:deploy to redeploy the environment
• ❌ /bns:delete to remove the environment