add: CLI support

[cdscih]

Ideally this tool would also have a CLI interface.

It's not supposed to be too hard to do, the Options object would simply need to be created through CLI params, but it's not of high priority since it's supposed to be a UI tool first.

Notes:

• this "bin feature" of the package.json seems very interesting for this purpose.
• I really like the CLI implementation of autocannon, we could take inspiration on how to do it there.