Clarify the type and number of Cloud Storage Operations performed by gcsfuse

Hi there,

I am trying debug a larger than expected number of [Cloud Storage Class A operations](https://cloud.google.com/storage/pricing#price-tables), and I'm wondering if my usage of `gcsfuse` may explain it.

Concretely, if I mount a bucket via `gcsfuse --implicit-dirs my-bucket /my-bucket` and then attempt to read a file in a somewhat deeply nested directory `/my-bucket/directory1/directory2/directory3/file`, how many Class A Operations would you expect this to make?

I expected the answer to be 0 (just a single `storage.objects.get`, which is a Class B operation), but from re-reading the [--implicit-dirs semantics](https://github.com/GoogleCloudPlatform/gcsfuse/blob/master/docs/semantics.md#implicit-directories), it looks like there will be at least one `storage.objects.list`.

Thanks for your help and for this useful utility.