Update SPM Package.swift

Author: djbe

Package.swift

@@ -1,5 +1,19 @@
+// swift-tools-version:4.0
 import PackageDescription
 
+// Note: SPM support is broken until we can add dependency on UIKit.
+
 let package = Package(
-    name: "Reusable"
+    name: "Reusable",
+    products: [
+        .library(name: "Reusable", targets: ["Reusable"])
+    ],
+    targets: [
+      .target(
+        name: "Reusable",
+        path: "",
+        sources: ["Sources"]
+      )
+    ],
+    swiftLanguageVersions: [3, 4]
 )