Add detail about explicit histogram buckets and boundaries (#1933)
Add detail about explicit histogram buckets and boundaries (#1933)

* Add detail about explicit histogram buckets and boundaries

* reword bucket counts

* nit

Co-authored-by: Josh Suereth <b62d57aa57da8c6c1773576bfb10d7e50207d7e0@google.com>
open-telemetry/opentelemetry-specification,open-telemetry/opentelemetry-specification