The documentation has been updated to clarify that future reservation requests don't support E2 machine types

## Change The documentation has been updated to clarify that future reservation requests don't support E2 machine types. To reserve VMs that use E2 machine types, use on-demand reservations instead. For more information, see [Restrictions on creation](https://cloud.google.com/compute/docs/instances/future-reservations-overview#restrictions-create).