Add better docs for psp clusters

[johscheuer]

Document what is required in order to run illuminatio in restricted clusters with psp.

See: #67

[maxbischoff]

Some small details, otherwise lgtm.

Should we simply provide a PodSecurityPolicy that contains these? Might be simpler than maintaining documentation in the long run. (I would still merge this and address it in a later PR if you agree)

[johscheuer]

I updated the docs and fixed the docker cli image to use a different user than root (and some other minor issues)

[johscheuer]

I created an issue for providing a PSP -> #73

IMHO if you run a Cluster with PSP activated you should be able to write it yourself since most tooling in the Kubernetres ecosystem probably doesn't provide them (which doesn't mean we shouldn't :))

[maxbischoff]

Minor changes again, thanks

[johscheuer]

@maxbischoff so good you need to approve twice ! 😂