readme: Make a statement about hiding node_modules from Spotlight

[merchako]

An intuitive off-label use of Asimov would be to prevent Spotlight from search */node_modules/. Indeed, I came across Asimov while searching for a way to get Spotlight to ignore these folders. At a glance, it's unclear whether Asimov would do this. Could you add a statement to /readme to clarify whether it would?