Add Package.swift

Package.swift

@@ -0,0 +1,48 @@
+// swift-tools-version:5.4
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+import PackageDescription
+
+let package = Package(
+    name: "json",
+    platforms: [
+        .iOS(.v9), .macOS(.v10_10), .tvOS(.v9), .watchOS(.v2)
+    ],
+    products: [
+        .library(
+            name: "json",
+            targets: ["json"]),
+    ],
+    targets: [
+        .target(
+            name: "json",
+            dependencies: [],
+            path: ".",
+            exclude:
+                [
+                    "appveyor.yml",
+                    "benchmarks",
+                    "cmake",
+                    "ChangeLog.md",
+                    "doc",
+                    "include",
+                    "test",
+                    "third_party",
+                    "CMakeLists.txt",
+                    "CODE_OF_CONDUCT.md",
+                    "LICENSE.MIT",
+                    "Makefile",
+                    "meson.build",
+                    "nlohmann_json.natvis",
+                    "README.md",
+                    "wsjcpp.yml",
+                ],
+            sources:
+                [
+                    "_SwiftPackageManagerFile.cpp"
+                ],
+            publicHeadersPath: "./single_include/nlohmann/")
+    ],
+    
+    cxxLanguageStandard: .cxx11
+)