Expand best practices around documenting values.yaml

[matt-carr]

Followup from https://github.com/helm/helm/issues/11787

My team went through a very long exercise of updating our values.yaml documentation and weren't sure what the best practices around nested values and subcharts were. These are our suggestions, based on what seemed to make sense at the time - naturally, open to suggestions, and even to ditch this whole thing in favour of a single line "use your best judgement with nested properties".

The intent is to match up as much as possible with the best practices laid out earlier - specifically, easily grep-able names

[matt-carr]

~bump~

[matt-carr]

🙃 bump 🙂