Add repo URL to generated file preamble

I am soon going to distribute json2swift as a binary, instead of having devs build the tool from source, so I’m adding a link to the tool’s GitHub repository. This will help people know where the tool came from, how to submit bug reports, request features, etc.

json2swift/swift-code-generation.swift

@@ -12,10 +12,7 @@ struct SwiftCodeGenerator {
     /// This method is used when only one Swift file is being generated.
     static func generateCodeWithJSONUtilities(for swiftStruct: SwiftStruct) -> String {
         return [
-            "// This file was generated by json2swift.",
-            "",
-            "import Foundation",
-            "",
+            preamble,
             "//",
             "// MARK: - Data Model",
             "//",
@@ -31,24 +28,24 @@ struct SwiftCodeGenerator {
     /// This method is used when multiple Swift files are being generated.
     static func generateCode(for swiftStruct: SwiftStruct) -> String {
         return [
-            "// This file was generated by json2swift.",
-            "",
-            "import Foundation",
-            "",
+            preamble,
             swiftStruct.toSwiftCode(),
             ""].joined(separator: "\n")
     }
 
     /// This method is used to only create the JSON utility code once when multiple Swift files are being generated.
     static func generateJSONUtilities() -> String {
         return [
-            "// This file was generated by json2swift.",
-            "",
-            "import Foundation",
-            "",
+            preamble,
             jsonUtilitiesTemplate,
             ""].joined(separator: "\n")
     }
+
+    private static let preamble = [
+        "// This file was generated by json2swift. https://github.com/ijoshsmith/json2swift",
+        "",
+        "import Foundation",
+        ""].joined(separator: "\n")
 }