Define library product

Author: klaaspieter

Package.swift

@@ -4,6 +4,9 @@ import PackageDescription
 
 let package = Package(
     name: "Docopt",
+    products: [
+      .library(name: "Docopt", targets: ["Docopt"])
+    ],
     targets: [
         .target(
             name: "Docopt",
@@ -17,4 +20,4 @@ let package = Package(
         //     path: "DocoptTests"
         // )
     ]
-)
+)