Update docker test README

test/docker/README.md

@@ -1,5 +1,7 @@
 # Docker database images to run ejabberd tests
 
+## Starting databases
+
 You can start the Docker environment with Docker Compose, from ejabberd repository root.
 
 The following command will launch MySQL, PostgreSQL, Redis and Riak, and keep the console
@@ -14,6 +16,16 @@ mkdir test/docker/db/riak/data
 
 You can stop all the databases with CTRL-C.
 
+## Running tests
+
+You can run tests with (from ejabberd repository root):
+
+```
+make test
+```
+
+## Cleaning up the test environment
+
 You can fully clean up the environment with:
 
 ```