Add details about deploying with CORS (#209)

demos/web-editor/README.md

@@ -13,5 +13,17 @@ npm run serve
 Or bundle files for distribution with
 
 ```
-npm run build
+npm run dist
+```
+
+The web application must be served with cross-origin isolation, because it uses
+[shared memory](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer#security_requirements)
+for multithreading.
+
+The demo server is configured to add those headers in `serve.json`.
+
+To serve the application with Apache, add the following to an `.htaccess` file:
+```
+Header add Cross-Origin-Embedder-Policy: "require-corp"
+Header add Cross-Origin-Opener-Policy: "same-origin"
 ```

demos/web-editor/web/src/index.ts

@@ -112,7 +112,7 @@ class App {
 
         const endTime = performance.now();
         document.getElementById("status").textContent =
-          `Rendered in ${endTime - this.start_time} ms`;
+          `Rendered in ${(endTime - this.start_time).toFixed(2)} ms`;
         break;
       }
       case ResponseKind.Script: {