fix: add short hint in tools/modules/update on how force rebuild (#3396)
fix: add short hint in tools/modules/update on how force rebuild (#3396)

I always forget exactly where I dropped the sentinel files.
kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe