Document which `flux` version to use

Due to a breaking change in flux, we are currently limited to Flux version 0.14.2. The documentation should be clear about this.

If people's flux version is too new, they will get errors like this one in their helmreleases:

  Conditions:
    Last Transition Time:  2021-07-15T10:11:00Z
    Message:               Helm uninstall failed: uninstall: Release not loaded: local-path-provisioner: release: not found

Last Helm logs:


    Reason:                UninstallFailed
    Status:                False
    Type:                  Ready
    Last Transition Time:  2021-07-15T11:11:00Z
    Message:               Helm install failed: error while running post render on files: map[string]interface {}(nil): yaml: unmarshal errors:
  line 15: mapping key "apiVersion" already defined at line 2
  line 16: mapping key "data" already defined at line 14

Last Helm logs:


    Reason:                InstallFailed
    Status:                False
    Type:                  Released
    Last Transition Time:  2021-07-15T11:11:01Z
    Message:               Helm uninstall failed: uninstall: Release not loaded: local-path-provisioner: release: not found

Last Helm logs:


    Reason:                        UninstallFailed
    Status:                        False
    Type:                          Remediated