Incorrect pressure level count in GraphCast_small checkpoint description

Hello,

I believe there's a small metadata error in the description of the `GraphCast_small` model checkpoint stored in GCS.

When loading the GraphCast_small checkpoint as demonstrated in the `graphcast_demo.ipynb` notebook, the model's internal description incorrectly states that it uses 37 pressure levels, while the filename and the actual model configuration confirm it uses 13 pressure levels.

Here is the internal description:
Low resolution version of the GraphCast model (1deg, smaller mesh), with **37 pressure levels**...

The description string within the `GraphCast_small` checkpoint file should be updated to state 13 pressure levels to avoid confusion.

Thank you!