Add note to waitgroups example about errgroup

Fixes #308

examples/waitgroups/waitgroups.go

@@ -39,4 +39,9 @@ func main() {
 	// Block until the WaitGroup counter goes back to 0;
 	// all the workers notified they're done.
 	wg.Wait()
+
+	// Note that this approach has no straightforward way
+	// to propagate errors from workers. For more
+	// advanced use cases, consider using the
+	// [errgroup package](https://pkg.go.dev/golang.org/x/sync/errgroup).
 }

examples/waitgroups/waitgroups.hash

@@ -1,2 +1,2 @@
-fd77f5122e6df1669c0a2e0d2c4dfbd30631c21f
-7mWXl0yVe6I
+b87ababcf7e1ce54107252c658840097bb6060a7
+vXBl8zQpDYj