doc: clarify options for fs.watchFile()
doc: clarify options for fs.watchFile()

The explanation for the `options` argument to `fs.watchFile()` had
missing punctuation. I took the opportunity to try to rewrite the
paragraph for greater clarity.

PR-URL: https://github.com/nodejs/node/pull/2425
Reviewed-By: Sakthipriyan Vairamani <b84950071fc99921a72f4fa56f6cad2496b3223c@gmail.com>
Reviewed-By: Brendan Ashworth <2a35967cb8cf8bc6bb9ebf86d18bb6cabb303f5b@me.com>

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node