docs: add Homebrew install instructions to the README

[gjtorikian]

The Homebrew channel shipped in #196 and workos/homebrew-tap now serves the 0.20.1 formula, but the README's Installation section only covered the GitHub Releases script and npm.

Adds:

brew install workos/tap/workos

and relabels the curl script as "direct download" to distinguish the two.

🤖 Generated with Claude Code

[greptile-apps]

Greptile Summary

Adds Homebrew installation instructions and clarifies the existing macOS/Linux script as the direct-download option.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
README.md	Documents brew install workos/tap/workos and distinguishes Homebrew from direct-download and npm installation methods.

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