Add iOS to platform description

Author: btoms20

Package.swift

@@ -18,7 +18,8 @@ import PackageDescription
 let package = Package(
     name: "swift-libp2p-identify",
     platforms: [
-        .macOS(.v10_15)
+        .macOS(.v10_15),
+        .iOS(.v13),
     ],
     products: [
         // Products define the executables and libraries a package produces, and make them visible to other packages.