NFC: clarify Target.publicHeadersPath comment (#2979)
NFC: clarify Target.publicHeadersPath comment (#2979)

The doc comment doesn't specify that the value of `publicHeadersPath` should be relative to the value specified in `path`.
abertelrud/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager,apple/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager