[docs] Update zookeeper-operator Helm chart configuration documentation (README)

[cbuto]

Description

Hello 👋 ! thanks for the awesome project. This should be a simple one (and I'm happy to contribute), I noticed there are a few missing configuration parameters from the zookeeper-operator chart README. It would be nice to have the missing parameters documented in that README.

Importance

This is really just a nice to have issue.

Location

https://github.com/pravega/zookeeper-operator/blob/master/charts/zookeeper-operator/README.md

Suggestions for an improvement

For now, updating the README manually with the missing configuration parameters should be good!

Thanks again!