Docs: Add Documentation for User Onboarding

**Is your feature request related to a problem? Please describe.**
Missing documentation for user management

**Describe the solution you'd like**
I as an admin would like to add new permission to users or groups. How should I do this and where should I store the configs declaring the permissions? What rolebindings should I use?

**Describe alternatives you've considered**
Refering to KCC documentation.