cmd/link: document that -s implies -w

Existing documentation does not reference implicit behavior.
Updates the documentation to reflect that -s implies -w.

Fixes #71051

Change-Id: I5c139c37f5f78596365e38479be4c865a4d4dd62
GitHub-Last-Rev: a3e462c4168284529ea1b0d03bc25fb1c12f1da5
GitHub-Pull-Request: golang/go#71053
Reviewed-on: https://go-review.googlesource.com/c/go/+/638976
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

src/cmd/link/doc.go

@@ -118,6 +118,7 @@ Flags:
 		Link with race detection libraries.
 	-s
 		Omit the symbol table and debug information.
+		Implies the -w flag, which can be negated with -w=0.
 	-tmpdir dir
 		Write temporary files to dir.
 		Temporary files are only used in external linking mode.