update readme

README.md

@@ -1,16 +1,7 @@
 # WebAssembly Playground
 
 - Write WebAssembly in the text mode, compile and run it in your browser.
-- Write JavaScript code to interact with WebAssembly, with visual previews.
+- Write JavaScript code to interact with WebAssembly, and to customize the preview.
 - Use WebAssembly post-MVP features.
 
 Try it at <https://yfzhe.github.io/webassembly-playground>.
-
-<details>
-  <summary>Development Notice</summary>
-
-  Service worker is available only in HTTPS context.
-  For local development, you can open chrome with flag
-  `--ignore-certificate-error`, to bypass the problem
-  that self-signed certificates are not trusted.
-</details>