Add doc about NodeJS being required

doc/0.getting_started.md

@@ -45,6 +45,10 @@ An alternative method is available using Docker. See [2.docker.md](2.docker.md).
    `npm install && npm run build:dev` (use `build:prod` in production).
 7. Use `python -m flatisfy serve --config config.json` to serve the web app.
 
+Note: `Flatisfy` requires an up-to-date Node version. You can find
+instructions on the [NodeJS website](https://nodejs.org/en/) to install latest
+LTS version.
+
 
 ## Available commands