chore: add license headers (#384)

* feat: check for license headers

* add headers

* format

plugins/window/build.rs

@@ -1,3 +1,7 @@
+// Copyright 2019-2023 Tauri Programme within The Commons Conservancy
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-License-Identifier: MIT
+
 fn main() {
     let target_os = std::env::var("CARGO_CFG_TARGET_OS").unwrap();
     let mobile = target_os == "ios" || target_os == "android";