update releases/<profile>.yaml based on what's really there

Created by: tomalok

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.