Add macOS installation document

[thomastthai]

Requirements

• I've searched platform-specific issues, issues and discussions to see if this has been reported before.
• My issue is unrelated to multiple key presses, OR it is and I've confirmed it is not key ghosting.

Describe the bug

I'd happily turn #1537 into a document for inclusion in docs/setup-macos.md and a reference in REAME.md. There are other configuration sections for macOS I'd like to add soon, e.g., #975 configuring function key OS actions or features such as brightness, Mission Control, Spotlight, and more, as indicated by icons on the keys.

Relevant kanata config

No response

To Reproduce

Missing macOS setup documentation.

Expected behavior

Have detailed macOS setup documentation.

Kanata version

1.8.0

Debug logs

No response

Operating system

macOS

Additional context

No response

[jtroo]

Sounds good to me!

[thomastthai]

@jtroo, the document has a lot of images. What's your preference in organizing the images along with the markdown file?

[jtroo]

Please put the images alongside the markdown file into a subdirectory of docs/, e.g. docs/macos-install/.