Add some comments

codecs/oxipng/worker.ts

@@ -11,6 +11,10 @@ addEventListener(
     //
     // At this point, the "main" thread can run Wasm that
     // will synchronously block waiting on other atomics.
+    //
+    // Note that we don't need to wait for Wasm instantiation here - it's
+    // better to start main thread as early as possible, and then it blocks
+    // on a shared atomic anyway until Worker is fully ready.
     postMessage(null);
 
     await initOxiPNG(...(event.data as WorkerInit));