Update week 4 README.md

Author: ry-v1

bootcamp/materials/4-apache-flink-training/README.md

@@ -104,7 +104,7 @@ cd bootcamp/materials/4-apache-flink-training
     make job
 
     #// if you dont have make, you can run:
-    # docker-compose exec jobmanager ./bin/flink run -py /opt/job/start_job.py -d
+    # docker-compose exec jobmanager ./bin/flink run -py /opt/src/job/start_job.py -d
     ```
 
     After about a minute, you should see a prompt that the job's been submitted (e.g., `Job has been submitted with JobID <job_id_number>`). Now go back to the [Flink UI](http://localhost:8081/#/job/running) to see the job running! :tada: