Add install.sh: automated macOS installer for Copilot for Xcode#5

Copilot wants to merge 2 commits intomainluisespersonal-byte/CopilotForXcode:mainfrom

copilot/resume-pull-request-againluisespersonal-byte/CopilotForXcode:copilot/resume-pull-request-againCopy head branch name to clipboard