fix remaining documentation links

PiperOrigin-RevId: 707545732
Change-Id: I7884743d0e4d0424a39e79a975827baafda14278
Reviewed-on: https://go-review.googlesource.com/c/open2opaque/+/637435
Auto-Submit: Michael Stapelberg <stapelberg@google.com>
Reviewed-by: Michael Stapelberg <stapelberg@google.com>
Reviewed-by: Chressie Himpel <chressie@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

internal/o2o/rewrite/rewrite.go

diff --git a/internal/o2o/rewrite/rewrite.go b/internal/o2o/rewrite/rewrite.go
index d763a4d..67cf9b0 100644
--- a/internal/o2o/rewrite/rewrite.go
+++ b/internal/o2o/rewrite/rewrite.go
@@ -67,7 +67,11 @@
 func (*Cmd) Usage() string {
 	return `Usage: open2opaque rewrite -levels=yellow <target> [<target>...]
 
-See http://godoc/3/net/proto2/go/open2opaque/open2opaque for documentation.
+For documentation, see:
+* https://go.dev/blog/protobuf-opaque
+* https://protobuf.dev/reference/go/opaque-migration/
+
+Report issues at https://github.com/golang/open2opaque/issues
 
 Command-line flag documentation follows:
 `
@@ -192,7 +196,7 @@
 		return err
 	}
 	if targetsKind == "unknown" {
-		return fmt.Errorf("could not detect target kind of %q - neither a blaze target, nor a .go file, nor a go package import path (see http://godoc/3/net/proto2/go/open2opaque/open2opaque for instructions)", targets[0])
+		return fmt.Errorf("could not detect target kind of %q - neither a blaze target, nor a .go file, nor a go package import path (see https://protobuf.dev/reference/go/opaque-migration/ for instructions)", targets[0])
 	}
 
 	inputTypeUses := targetsKind == kindTypeUsages