net: mention the cgo thread limit in package docs
Updates #63978
Change-Id: I39a5c812b4f604baf4ca5ffcff52b8dc17d4990d
GitHub-Last-Rev:
4ab6e262f4fd37ff32d6b3eb756fea187e5d6e53
GitHub-Pull-Request: golang/go#63990
Reviewed-on: https://go-review.googlesource.com/c/go/+/539361
Reviewed-by: 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: Roland Shoemaker <roland@golang.org>