Allow adding more values.yaml

[zalsader]

Since helmify always overwrites values.yaml, any additional values I would like to add get removed. One way to solve this would be to add an option where a file containing additional values is appeneded to the values.yaml file. Basically What I'd like to do is:

cat my-app.yaml | helmify -additional-values=additionalValues.yaml mychart

Which would be effectively equivalent to:

cat my-app.yaml | helmify mychart
cat additionalValues.yaml >> mychart/values.yaml

Alternatively, it would be nice if the values.yaml was edited instead of overwritten, since I would also like to add comments and use tools like helm-docs