reflect: clarify documentation for Value.Seq/Seq2
For #66056
Change-Id: Ib47c07b2527d8213584b72e2575a353f2deaed68
GitHub-Last-Rev:
525a5c3fa469fcccfb1ab67b61c7d12e024cfb33
GitHub-Pull-Request: golang/go#67268
Reviewed-on: https://go-review.googlesource.com/c/go/+/584515
Reviewed-by: Cherry Mui <cherryyz@google.com>
Commit-Queue: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>