More obvious docs for watching network mounts

README.md

@@ -122,9 +122,10 @@ derived. Paths emitted with events will be relative to this.
 polling for binary files (see extensions in src/is-binary).
 * `usePolling` (default: `false`).
 Whether to use fs.watchFile (backed by polling), or fs.watch. If polling
-leads to high CPU utilization, consider setting this to `false`. Polling
-may be necessary to successfully watch files in certain situations, such as
-network mounted drives. Setting to `true` explicitly on OS X overrides the
+leads to high CPU utilization, consider setting this to `false`. It is
+typically necessary to **set this to `true` to successfully watch files over
+a network**, and it may be necessary to successfully watch files in other
+non-standard situations. Setting to `true` explicitly on OS X overrides the
 `useFsEvents` default.
 * `useFsEvents` (default: `true` on OS X). Whether to use the
 `fsevents` watching interface if available. When set to `true` explicitly