Use the package.json description if no description returned from a command

[matt-gadd]

Enhancement
We're using the description from the package.json when using the search capabilities to show available commands to install. Perhaps we should use the package.json description for the actual command itself also? At the moment it is currently returned from the command like so: https://github.com/dojo/cli-build-app/blob/master/src/main.ts#L161