adding in script for serve

package.json

@@ -31,6 +31,7 @@
     "clean": "rimraf ./dist ./coverage ./node_modules ./package-lock.json ./yarn.lock",
     "build": "rimraf ./dist && tsc",
     "test": "xo --fix && vitest run --coverage",
+    "serve": "node bin/writr.mjs serve -s ./site -o ./dist/site-output",
     "prepare": "yarn run build"
   },
   "bin": {