feat: option to trigger command on startup

[privatenumber]

Problem

I'd like for the command to run as I start the watch eg. running a test.

Currently, I have to trigger a blank save to make it run.

Feature request

An -i, --initial or --leading flag (like lodash's debounce), to invoke the command on startup.

[cometkim]

eg. running a test.

I'm using {command} || true && watchlist {...files} -- {command} for this.