update readme
added description about trailing underscore convention
During the maintenance period on Monday, 14 Oct 2024, all new projects will no longer create a container registry as part of the project area. Already existing projects will be unaffected at this time. Instead, users should utilize the official ORNL container registries at camden.ornl.gov (internal/moderate) and savannah.ornl.gov (external/low). Please see ORNL Today article for more info.
added description about trailing underscore convention