Add dev script

Author: LeaVerou

package.json

@@ -10,6 +10,7 @@
     "build:docs": "npx typedoc",
     "watch:docs": "npx typedoc --watch --preserveWatchOutput",
     "watch": "npm run watch:html",
+    "dev": "npx @11ty/eleventy --config=_build/eleventy.js --serve",
     "eslint": "npx eslint .",
     "eslint:fix": "npx eslint . --fix",
     "release": "release-it"