Add serve config & more instructions

README.md

@@ -1,3 +1,8 @@
-To build, you'll need Docker. Run `./build.sh` and it should do the rest.
+To build, you'll need Docker. Then:
 
-Then, start a local HTTP server and navigate to `http://localhost:port/ui/`.
+```bash
+./build.sh # runs build in Docker for libapi.{mjs,wasm,worker.js}
+serve . # starts a local server with COOP/COEP
+```
+
+Then, navigate to http://localhost:5000/ui/ in Chrome.