format: reword deprecate notice and use doc links

pkg/strings/strings.go

@@ -2,7 +2,7 @@ package strings
 
 import "slices"
 
-// Deprecated: Use go slices package instead.
+// Deprecated: Use standard library [slices.Contains] instead.
 func Contains(list []string, needle string) bool {
 	// TODO(v4): remove package.
 	return slices.Contains(list, needle)