[doc] update hyperlink (#16877)

Signed-off-by: reidliu41 <reid201711@gmail.com>
Co-authored-by: reidliu41 <reid201711@gmail.com>

docs/source/models/extensions/fastsafetensor.md

 Loading Model weights with fastsafetensors
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-Using fastsafetensor library enables loading model weights to GPU memory by leveraging GPU direct storage. See https://github.com/foundation-model-stack/fastsafetensors for more details.
+Using fastsafetensors library enables loading model weights to GPU memory by leveraging GPU direct storage. See [their GitHub repository](https://github.com/foundation-model-stack/fastsafetensors) for more details.
 For enabling this feature, set the environment variable ``USE_FASTSAFETENSOR`` to ``true``