Removing some installation instructions

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | no
| Applies to    | all
| Fixed tickets | n/a

Hi guys!

This removes some duplicate installation instructions. I want less docs, without explaining less :). Duplicate like this is an opportunity to give users more paths for no reason. I'm sure we have more things like this - like details on handling parameters.yml or other things.

Thanks!
Maybe we could create a short list of instructions for people using the installer and then an additional list of things that you need to know in case you didn't use the installer.