Update README.md (update EnvFactoryRegistered params) (#1228)

To initiate a EnvFactoryRegistered, we now need `train_seed=0` and
`test_seed=0` arguments passed instead of `seed` previously written in
documentation code snippet.

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README.md

@@ -236,7 +236,7 @@ almost exclusively concerned with configuration that controls what to do
 ```python
 experiment = (
     DQNExperimentBuilder(
-        EnvFactoryRegistered(task="CartPole-v1", seed=0, venv_type=VectorEnvType.DUMMY),
+        EnvFactoryRegistered(task="CartPole-v1", train_seed=0, test_seed=0, venv_type=VectorEnvType.DUMMY),
         ExperimentConfig(
             persistence_enabled=False,
             watch=True,