chore: add script notes for SFC playgound [ci skip]

Author: yyx990803

packages/sfc-playground/README.md

@@ -1,3 +1,19 @@
-## SFC Playground
+# SFC Playground
 
-This is continuously deployed at [https://sfc.vuejs.org](https://sfc.vuejs.org).
+This is continuously deployed at [https://sfc.vuejs.org](https://sfc.vuejs.org).
+
+## Run Locally in Dev
+
+In repo root:
+
+```sh
+pnpm dev-sfc
+```
+
+## Build for Prod
+
+In repo root
+
+```sh
+pnpm build-sfc-playground
+```