Update links in Usage.md

Author: ElektrojungeAtWork

Documentation/Usage.md

@@ -48,7 +48,7 @@ get started, create a directory and run `swift package init` command:
 This will create the directory structure needed for a library package with a
 target and the corresponding test target to write unit tests. A library package
 can contain multiple targets as explained in [Target Format
-Reference](PackageDescriptionV4.md#target-format-reference).
+Reference](PackageDescription.md#target).
 
 ### Create an executable package
 
@@ -65,7 +65,7 @@ get started:
 This creates the directory structure needed for executable targets. Any target
 can be turned into a executable target if there is a `main.swift` present in
 its sources. Complete reference for layout is
-[here](PackageDescriptionV4.md#target-format-reference).
+[here](PackageDescription.md#target).
 
 ## Define Dependencies