Fixed README.md [#CLICKHOUSE-2821]

dbms/tests/integration/README.md

@@ -10,7 +10,7 @@ Prerequisites:
 * [docker-compose](https://docs.docker.com/compose/). To install: `sudo pip install docker-compose`
 * [py.test](https://docs.pytest.org/) testing framework. To install: `sudo pip install pytest`
 
-If you want to run the tests under a non-privileged user, you must add this user to `docker` group: `sudo usermod -aG docker $USER`.
+If you want to run the tests under a non-privileged user, you must add this user to `docker` group: `sudo usermod -aG docker $USER` and re-login.
 
 Run the tests with the `pytest` command. To select which tests to run, use: `pytest -k <test_name_pattern>`