Add prerequisites section to README.md

README.md

@@ -3,6 +3,7 @@
 ## Table of contents
 
 - [Project structure](#project-structure)
+- [Prerequisites](#prerequisites)
 - [Overview](#overview)
 - [Deployment](#deployment)
 - [Getting started](#getting-started)
@@ -53,6 +54,18 @@
  └─ Vagrantfile  # Virtual machine configurations
 ```
 
+## Prerequisites
+
+- Vagrant, to run the virtual machines
+
+### Optional dependencies
+
+- JDK 15, to compile the backend code outside of a provisioned virtual machine. Higher versions
+  should be fine as well but are not released at the time of writing
+- Maven, to package the frontend and backend parts into a JAR. The provided Maven wrapper `mvnw`
+  may be used instead
+- CockroachDB, if one wants to run the packaged JAR outside of a provisioned virtual machine
+
 ## Overview
 
 This project realizes a basic URL shortener using Spring on the backend and Angular on the frontend.