net/rpc: clarify documention of Call.Done field
net/rpc: clarify documention of Call.Done field

Fixes #36116

Change-Id: I93909f2addee9a9435ad658e8b40eef966ce53fe
Reviewed-on: https://go-review.googlesource.com/c/go/+/238078
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Josh Bleecher Snyder <cdc248cc4d32e4fbfe04e45228163bcecd48a0b9@gmail.com>

cloudflare/go,cloudflare/go,CAFxX/go,golang/go,CAFxX/go,golang/go,golang/go,cloudflare/go,nawawi/go,golang/go,CAFxX/go,cloudflare/go,nawawi/go,nawawi/go,nawawi/go,nawawi/go,CAFxX/go,CAFxX/go,CAFxX/go,golang/go,cloudflare/go,golang/go,cloudflare/go,golang/go,nawawi/go,golang/go,cloudflare/go,CAFxX/go,nawawi/go,nawawi/go,CAFxX/go,cloudflare/go