Add README.md with required envs to the spring-app

[Kuboczoch]

While developing on multiple devices, I ran into an issue where I need to add some environments to my spring run configuration.

It would be nice to have a document telling me what environments I need to add. Right now if I don't add anything then the app won't start on it's own.

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Another option is to implement files for the running environment as we are doing it right now on the frontend side.

For example; for dev env we do have a file named .env.development and for the production .env.production which is a very simple way to store your envs that can change depending on which way you are using the app.