Support updates

[kiliankoe]

See https://github.com/BenchR267/goalfred/issues/8

Ideally this would include having a little more structure to the CLI being built as a worklow, not unlike swift-argument-parser, with a well-defined entry point that does some more work in the background. Since a workflow contains some more data than just the Swift code, it might not be possible to just pull a package from a git repo and build it locally. Ideally the end user also wouldn't have to have the swift toolchain installed. So it would probably make sense to focus on GitHub releases as a first step. The tool would check for a new release in the background when the workflow is run, prompt to update if it exists pulling the new release and replacing the current workflow with it. Make sure to not be dependent on the user keeping Alfred open here (which is probably the default behavior - just guessing).

The workflow developer would have to provide a git URL, anything else?