chore(build): try to build demo and docs (#3434)

platform/app/.env.example

@@ -0,0 +1,10 @@
+##
+# EXAMPLE
+#
+# Read more about .env files when using create-react-app here:
+# https://facebook.github.io/create-react-app/docs/adding-custom-environment-variables#adding-development-environment-variables-in-env
+#
+
+PUBLIC_URL=/demo/
+APP_CONFIG=config/netlify.js
+USE_HASH_ROUTER=false