To save cache json requires a clean exit of the process.

.cache-require-paths.json was not getting created.
Looked at code seems that a clean exist needs to be had but when adding it to an existing project that listens on sockets and serves http requests etc it does not exit normally.

Save cache after a timeout of say 5 seconds with an option to increase this time?
Or maybe add a saveCache method?

The note in readme would be better placed under the Use section.

```Note that the speedup only happens after the first application run finishes successfully and the process exits. The resolution cache needs to be saved to a local file, and this happens only on process exit.```