API key documentation

[Haavi97]

env file comment says (leave empty to disable, or set to secure value) but leaving it empty still requires API key. I think that is reasonable.
My suggestion:

• Update documentation about API key
• Add a simple script that generates a secure random API key

[Haavi97]

oK, I understood you have to look for the API key in the container files (if you haven't added it in the .env before composing). From this: #89

Also, in the get started guide:
You can also create new keys via the API (see API Specification).
But there's nothing there to create an API key. It should reference to api/auth/api-keys endpoint