update Helm docs with latest behaviour

[dminca]

Update readme to address regression bug that doesn't automatically
trigger HelmRelease deployment if
-> the full Docker Registry URL + image name + image label are not provided
in a Helm Chart as a single variable (not splitted)
-> which in turn is read by the HelmRelease

Resolves:
Related: #2067
Signed-off-by: Daniel Andrei Minca

[hiddeco]

The split format should work fine, the issue with the format in #2067 is that

image:
  registry: marcel-registry.com/myapp
  tag: master-3d30e14fd7

should be

image:
  repository: marcel-registry.com/myapp
  tag: master-3d30e14fd7

as documented here.

[dminca]

Ok, now it makes sense. I'll test and if it doesn't work out well I'll reopen this one.

Thanks 👍