update releases/<profile>.yaml based on what's really there
Perhaps the new
release subcommand could also traverse the regions and update
releases/<profile>.yaml with the matching AMIs that actually exist there.
Or, the same broker mechanism used in
release could be used in a different subcommand.
No/few changes to the code to update
releases/README.md should be necessary as long as the release's YAML is fully fleshed out.