Fix pip install instruction in README

Rename `huggingface_transfer` to `hf_transfer`.

README.md

@@ -21,7 +21,7 @@ How to use with [MLX](https://github.com/ml-explore/mlx).
 
 # Install mlx, mlx-examples, huggingface-cli
 pip install mlx
-pip install huggingface_hub huggingface_transfer
+pip install huggingface_hub hf_transfer
 git clone https://github.com/ml-explore/mlx-examples.git
 
 # Download model