no `global.existingSecret` format documentation

[deefdragon]

Many of the important values that need to be set are secrets such as passwords. The chart supports putting these in a k8s secret via global.existingSecret instead of in the helm values, but has no documentation as to the expected format necessary. This makes it very difficult to know what keys to use for the secret, and what values.

Please add documentation for the format of global.existingSecret to the readme. (I assume its just to set the associated variables here, but having that linked where its referenced would be useful)

[jdenquin]

hey @deefdragon , y're right all the values are in the doc, but it makes sense to add them here to ease the usage of existingSecret.
Please note that for now, only few of them are under the existingSecret condition.

[deefdragon]

Yeah, if only some of the environment variables are under existingSecret, those really need to be documented.