docs: clarify action state and normalizer expectations

[Rohithmatham12]

Summary

• clarify that inverse dynamics predicts action trajectories but does not synthesize full LeRobot observation.state records
• point users to the checked-in DROID LeRobot sample metadata for timestep-aligned state streams
• document that current action-layout and normalization references are the checked-in AV, DROID, and UMI assets/notebooks until additional embodiment assets are released

Why
Issue #192 asks how to obtain observation.state alongside predicted actions for LeRobot-format episodes. Issue #184 asks for action channel layouts and normalizers across embodiments. This PR documents the current supported boundary and points to the concrete checked-in sample without claiming unreleased embodiment-specific layouts.

Testing

• git diff --check

Addresses #192
Related to #184

[mli0603]

Thanks @Rohithmatham12. Will consolidate the your PR and the docs! We have a PR landing soon and we will take a look.