message: explain need for TEST_POOL_IP when running tests in some environments
diff: docker run -d --ip="10.0.0.2" --net=indy_pool_network indy_pool
  ```
  + If you use this method then you have to specify the TEST_POOL_IP as specified below when running the tests.
  +
  It can be useful if we want to launch integration tests inside another container attached to
  the same docker network.
  