[Documentation] Fix broken links to Target Format Reference in Usage.md (#1350)
[Documentation] Fix broken links to Target Format Reference in Usage.md (#1350)

* Fix broken links to Target Format Reference

* Update Target Format Reference link to V4 version.

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