linux-explicit-synchronization: Clarify implicit synchronization guarantees of release events

Clarify that after zwp_buffer_release_v1 events, otherwise unused
buffers can be reused without any additional implicit synchronization.
This is in contrast to wl_buffer.release, which doesn't guarantee that
implicit synchronization is not required to safely use a buffer after
the event is received.

Signed-off-by: Alexandros Frantzis <alexandros.frantzis@collabora.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.com>