[Doc] Add tuto and time dim info in docs (#1130)

Author: vmoens

docs/source/index.rst

@@ -49,6 +49,7 @@ Intermediate
    tutorials/torchrl_envs
    tutorials/pretrained_models
    tutorials/dqn_with_rnn
+   tutorials/rb_tutorial
 
 Advanced
 --------

docs/source/reference/envs.rst

@@ -63,6 +63,9 @@ With these, the following methods are implemented:
   a maximum number of steps (``max_steps=N``) and using a policy (``policy=model``).
   The policy should be coded using a :class:`tensordict.nn.TensorDictModule`
   (or any other :class:`tensordict.TensorDict`-compatible module).
+  The resulting :class:`tensordict.TensorDict` instance will be marked with
+  a trailing ``"time"`` named dimension that can be used by other modules
+  to treat this batched dimension as it should.
 
 The following figure summarizes how a rollout is executed in torchrl.
 

tutorials/sphinx-tutorials/rb_tutorial.py

@@ -491,7 +491,7 @@ class MyData:
 # sampled items:
 #
 sample = rb.sample()
-sample["td_error"] = (data.numel() - sample["index"]).exp()
+sample["td_error"] = data.numel() - sample["index"]
 rb.update_tensordict_priority(sample)
 
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