fix README file by providing correct instruction

[josephca]

Minor bugs need to be fixed in readme,

• helm upgrade -i oci://ghcr.io/janus-idp/helm-backstage/backstage --version=<version> should be updated to helm upgrade -i <release-name> oci://ghcr.io/janus-idp/helm-backstage/backstage --version=<version>
• when installing from oci repository, a user needs to set HELM_EXPERIMENTAL_OCI=1 to avoid installation errors. It would be nicer to have the instruction in README. However, the error message contains the correct instruction to fix the error :

  Installing janus backstage on OpenShift
  Error: this feature has been marked as experimental and is not enabled by default. Please set HELM_EXPERIMENTAL_OCI=1 in your environment to use this feature

[tumido]

Hi @josephca, thanks for raising this issue.

1. Yes, the release name should be updated in the README, I'll update it. Thank you! 🙂
2. The HELM_EXPERIMANTAL_OCI flag is deprecated since Helm v3.8.0 which was released in January of 2022. That is a year and a half ago. (See: https://helm.sh/docs/topics/registries/, https://github.com/helm/helm/releases/tag/v3.8.0). I don't think we should advise users on this since we don't aim to support every Helm version, so this should be safe to omit from the README.

[josephca]

@tumido I found one more place which may require a fix. From https://github.com/janus-idp/helm-backstage/blob/main/charts/backstage/README.md, at the end of the readme

upstream: backstage: -> it's missing appConfig: app:

[tumido]

I've updated the PR. Thank you for noticing 👍 🙂