Link Physical AI section to collection

Hyperlinks the Physical AI section header to https://huggingface.co/collections/nvidia/physical-ai for direct navigation to the collection.

README.md

@@ -59,7 +59,7 @@ NVIDIA releases optimized and aligned versions of leading community architecture
 * [**Llama-3.1-Nemotron**](https://huggingface.co/collections/nvidia/llama-nemotron)**:** A diverse family of models where Llama 3.1 architectures are fine-tuned using NVIDIA's **HelpSteer2** datasets to improve helpfulness and instruction adherence. Includes [Ultra (253B)](https://huggingface.co/nvidia/Llama-3_1-Nemotron-Ultra-253B-v1), [Super (49B)](https://huggingface.co/nvidia/Llama-3.3-Nemotron-Super-49B-v1), and [Nano (8B)](https://huggingface.co/nvidia/Llama-3.1-Nemotron-Nano-8B-v1) variants.  
 * **Mistral-NeMo:** A 12B parameter model built in collaboration with Mistral AI, offering a high performance-to-size ratio and an expanded 128k context window.
 
-## **Physical AI**
+## **[Physical AI](https://huggingface.co/collections/nvidia/physical-ai)**
 
 ### **NVIDIA Cosmos**