"Watch" mode for `make subo`

[MacklinEngineering]

Now, if you make a code change in Subo, you have to re run make subo which can become comberson to developers.

Automatically running make subo upon save of all files within subo would make the process smoother.

[ospencer]

We likely would want a specific make command to watch file changes, something like make subo/watch rather than trying to get make itself to re-execute!

Something like https://github.com/mitranim/gow could work, but that requires users to already have it installed on their machines. This would probably take some research to get right.

@cohix would something like a make subo/watch command make sense?