[Collections] Documentation (#3306)
[Collections] Documentation (#3306)

Collections Documentation

Document for SwiftPM users how to use the `package-collection` CLI and the signing-related errors that they might see, and for collection publishers how to generate and sign collections, as well as the certificate-pinning config.

apple/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,abertelrud/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager