docs: document integer granularity
docs: document integer granularity

Updates #334

Change-Id: Ia3f84971300d06c7b6f83c9399254af7f3bcedb9
Reviewed-on: https://code-review.googlesource.com/c/google-api-go-client/+/41870
Reviewed-by: Tyler Bui-Palsulich <b41e4aa57d2ad7eb1b29835a1b483e209dcc3c0e@google.com>

googleapis/google-api-go-client,google/google-api-go-client,googleapis/google-api-go-client,google/google-api-go-client