Add comment on Service-Worker-Allowed header

Author: code-asher

src/node/routes/index.ts

@@ -130,6 +130,9 @@ export const register = async (app: App, args: DefaultedArgs): Promise<Disposabl
       cacheControl: commit !== "development",
       fallthrough: false,
       setHeaders: (res, path, stat) => {
+        // The service worker is served from a sub-path on the static route so
+        // this is required to allow it to register a higher scope (by default
+        // the browser only allows it to register from its own path or lower).
         if (path.endsWith("/serviceWorker.js")) {
           res.setHeader("Service-Worker-Allowed", "/")
         }