Hopefully this gives users a better understanding of the MarshalAppend
entrypoint and what it can be used for, as well as the typical Size usage.
Change-Id: I26c9705c3d1dbfea5f30820d41ccabbb88fbb772
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/573361
Reviewed-by: Lasse Folger <lassefolger@google.com>
Auto-Submit: Michael Stapelberg <stapelberg@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cassondra Foesch <cfoesch@gmail.com>
Reviewed-by: Damien Neil <dneil@google.com>
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