Update usage for --init

Author: aciidgh

Sources/swift-build/usage.swift

@@ -20,7 +20,7 @@ func usage(print: (String) -> Void = { print($0) }) {
     print("MODES:")
     print("  --configuration <value>  Build with configuration (debug|release) [-c]")
     print("  --clean[=<mode>]         Delete artefacts (build|dist) [-k]")
-    print("  --init                   Creates a new Swift project")
+    print("  --init <mode>            Creates a new Swift package (exec|library)")
     print("  --fetch                  Fetch package dependencies")
     print("")
     print("OPTIONS:")