Document partial / reusable configuration

[marcinc]

Create quick walk through docs showing how to extract common bits of configuration and apply them automatically to multiple services.

Partials:

&default-resources
cpu: 0.1
max-cpu: 1
memory: 10Mi
max-memory: 500Mi

services:
    postfacto:
      x-k8s:
       resource: *default-resources
    other-service:
      x-k8s:
        resource: *default-resources