Simple waiting feedback for leo

[dacbd]

adds some simple feedback for when users run leo read --follow right after a leo create and there aren't any logs yet.

[0x2b3bfa0]

Please print to os.Stderr

[tasdomas]

Please print to os.Stderr

Is that really necessary? In this case the output is purely for UX, stdout is perfectly valid.

Granted, leo could use a quiet mode that's more automation friendly, but we've got more pressing issues

[0x2b3bfa0]

Currently leo read only outputs script logs to standard output, and all the other user-oriented messages to standard error. While we still don't provide any stability guarantees, it would be nice to stick to that principle.