Add brew installation to README

[louisunlimited]

Describe the feature or problem you'd like to solve

Looks like Copilot CLI is installable via brew as a cask but is not listed here.
Formula url

Getting release tar from

url "https://github.com/github/copilot-cli/releases/download/v#{version}/copilot-#{os}-#{arch}.tar.gz"

PR for that

• copilot-cli 0.0.366-8 (new cask) Homebrew/homebrew-cask#239114

Proposed solution

Adding a brew install would allow users to install copilot without a node env.

Example prompts or workflows

No response

Additional context

No response

[devm33]

Thanks @louisunlimited this will be added to the readme in the next stable release