docs: add macOS install guide

[fengfeng-zi]

Closes #3

• add a focused newcomer-friendly macOS install guide
• document source build and packaging entry points
• keep the change documentation-only

[TheNorthStarYang]

Thanks for the contribution! The macOS install guide is helpful and the commands/paths look generally aligned with the current project structure.

However, we’re trying to avoid adding platform-specific full install guides under the top-level docs/ directory, because it can easily create multiple sources of truth and make the documentation harder to maintain over time.

For this repository, we’d like to keep:

• docs/installation.md as the repo-level install/build entry point
• platforms/macos/README.md as the macOS platform overview
• platforms/macos/client/README.md as the main source of truth for macOS client build and packaging instructions

So instead of adding a new docs/install-macos.md, could you please update the existing docs by either:

1. adding a short macOS entry/link in docs/installation.md, or
2. improving/linking to platforms/macos/client/README.md for the detailed macOS client instructions?

This is mainly about keeping the documentation structure clean and avoiding doc drift. Thanks again for helping improve the project!

For now, I’ll hold off on merging this PR until the macOS guide is moved or consolidated into the existing documentation structure.

[fengfeng-zi]

Thanks for the review. I removed docs/install-macos.md and folded the macOS install docs back into the existing structure.

Changes made:

• added a short macOS docs entry in docs/installation.md
• added an installation-docs pointer section in platforms/macos/README.md
• kept the detailed build/package instructions under platforms/macos/client/README.md

This keeps the macOS guidance within the existing repo layout instead of a standalone top-level install page.