website/developer-docs: add note for node16 and npm i for api

Signed-off-by: Jens Langhammer <jens.langhammer@beryju.org>

website/developer-docs/frontend-only-dev-environment.md

@@ -4,6 +4,14 @@ title: Frontend-only development environment
 
 If you want to only make changes on the UI, you don't need a backend running from source. You can user the docker-compose install with a few customizations.
 
+### Prerequisites
+
+- Node (any recent version should work, we use 16.x to build)
+- Make (again, any recent version should work)
+- Docker and docker-compose
+
+### Instructions
+
 1. Clone the git repo from https://github.com/goauthentik/authentik
 2. In the cloned repository, follow the docker-compose installation instructions [here](/docs/installation/docker-compose)
 3. Add the following entry to your `.env` file: