differentiable physics tutorial missing module brax

[fanminshi]

When I run the Imports and installations section of differentiable physics tutorial I am getting the following import error

ModuleNotFoundError                       Traceback (most recent call last)
[<ipython-input-10-b1c0dcecae40>](https://localhost:8080/#) in <cell line: 14>()
     12 config.update("jax_enable_x64", True)
     13 config.update('jax_default_matmul_precision', jax.lax.Precision.HIGH)
---> 14 from brax import math
     15 
     16 # Sim

ModuleNotFoundError: No module named 'brax'

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NOTE: If your import is failing due to a missing package, you can
manually install dependencies using either !pip or !apt.

To view examples of installing some common dependencies, click the
"Open Examples" button below.
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I think the noteboot forgot to provide instruction to install brax

!pip install brax

[fanminshi]

I will submit a fix for this.