Fix adder documentation in components.md.
@@ -243,7 +243,7 @@ Example usage of an adder:
```python
# Reset the environment and add the first observation.
timestep = env.reset()
-adder.add_first(timestep.observation)
+adder.add_first(timestep)
while not timestep.last():
# Generate an action from the policy and step the environment.
