Update Readme

The following discussion from !345 (merged) should be addressed:

• @nils.brinckmann started a discussion: (+1 comment)

  I think in regard to the env variables we should update the orchestration readme additionally.

  There are still links to the frontend & backend repo that are no longer relevant.

  If you think it is a super small thing, we can do that here too. Otherwise I would suggest that we create another issue for this task & do that separately in the near future.