Clarify setup for multiple packages in a monorepo in docs#48

I know that turbowatch was motivated by challenges working in a monorepo, but the available examples don't really cover how you would do something like setting up build watches for an app's dependencies then triggering app restarts after they finish building. I see two options, but it's not clear what the implications would be for choosing to use multiple projects versus multiple triggers. I started off with looking into the latter option because I like the idea of managing all the watch tasks in one place, but I don't see how you can change the working directory for the commands that are run in the trigger, for example, running `tsc` inside of a dependency directory. This makes me think that maybe the pattern is instead to have multiple `turbowatch.ts` files, one for each package in a monorepo, but that seems like it might be harder to maintain than one project with multiple triggers. ## Desired Behavior There might be a few things that would make it easier to get started: * Link to an example monorepo project showcasing recommended practices * Describe when you would use multiple triggers versus multiple turbowatch files * Explain how `spawn` works in better details. Is it just a copy of the `$` object from `zx`? Is there a way to access the `cd` function from `zx`, or is `spawn` the only thing available for running commands? Can you run `cd` inside of the spawn command, an if you do so is the CWD scoped to the invoke of your trigger or is it a global context? Side note, it'd be nice if you could just specify a working directory on an individual trigger level. ## Motivation The docs are pretty good for showing how to set up a single watch task, but it'd be good to see a clear setup for how to use in a monorepo, leaning heavily on "typical" tasks like linting and `tsc`.