document some deployment options

[hall]

One of kubenix's main goals is to create resource manifests. While there's a basic CLI included for simple use-cases (e.g., my own), there are several, more robust and featureful, approaches using the plethora of tools from the broader community. I'd like to document some of these options for users; things like Adrian described here:

• decrypting secrets from within a cluster
• using a gitops-based approach

It doesn't have to be anything terribly detailed. Mostly a general guide of what's possible and why someone might pick one approach over another.