Merge pull request lit#9 from pmcelhaney/clarify-npm-run-build-on-guide

add npm run build (noop with a helpful message)

package.json

@@ -21,7 +21,8 @@
     "test:watch": "karma start karma.conf.cjs --auto-watch=true --single-run=false",
     "test:update-snapshots": "karma start karma.conf.cjs --update-snapshots",
     "test:prune-snapshots": "karma start karma.conf.cjs --prune-snapshots",
-    "checksize": "rollup -c ; cat my-element.bundled.js | gzip -9 | wc -c ; rm my-element.bundled.js"
+    "checksize": "rollup -c ; cat my-element.bundled.js | gzip -9 | wc -c ; rm my-element.bundled.js",
+    "build": "echo \"This is not a TypeScript project, so no need to build.\""
   },
   "keywords": [
     "web-components",