Update rust/pub-sub/README.md

Co-authored-by: Marco Walz <8124114+marc0olo@users.noreply.github.com>

Author: jessiemongeon1

rust/pub-sub/README.md

@@ -30,7 +30,7 @@ dfx canister id publisher
 ## Step 3: Subscribe to the "Apples" topic
 
 ```bash
-dfx canister call subscriber setup_subscribe '(principal "<publisher ID from Step 3>", "Apples")'
+dfx canister call subscriber setup_subscribe '(principal "<publisher ID from Step 2>", "Apples")'
 ```
 
 ## Step 4: Publish to the "Apples" topic