docs: Document CUDA version support in README and installation page (#2197)

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## 📌 Description

Add this to public docs CUDA version support 12.6, 12.8, 13.0, 13.1 and
state that our goal is to follow PyTorch support + latest CUDA version


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## Summary by CodeRabbit

* **Documentation**
* Updated CUDA support documentation with explicit supported versions:
12.6, 12.8, 13.0, and 13.1.
  * Documented CUDA version prerequisites for installation.
* Added clarification that supported CUDA versions align with PyTorch's
officially supported versions and the latest CUDA release.
  * Enhanced GPU support section header for better clarity.

<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>

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Author: bkryu

README.md

@@ -187,10 +187,14 @@ For detailed information about logging levels, configuration, and advanced featu
 
 Starting from FlashInfer v0.2, users can customize their own attention variants with additional parameters. For more details, refer to our [JIT examples](https://github.com/flashinfer-ai/flashinfer/blob/main/tests/utils/test_jit_example.py).
 
-## GPU Support
+## GPU and CUDA Support
 
 FlashInfer currently provides support for NVIDIA SM architectures 75 and higher and beta support for 103, 110, 120, and 121.
 
+**Supported CUDA Versions:** 12.6, 12.8, 13.0, 13.1
+
+> **Note:** FlashInfer strives to follow PyTorch's supported CUDA versions plus the latest CUDA release.
+
 ## Adoption
 
 We are thrilled to share that FlashInfer is being adopted by many cutting-edge projects, including but not limited to:

docs/installation.rst

@@ -15,6 +15,11 @@ Prerequisites
 
 - Python: 3.10, 3.11, 3.12, 3.13, 3.14
 
+- CUDA: 12.6, 12.8, 13.0, 13.1
+
+.. note::
+   FlashInfer strives to follow PyTorch's supported CUDA versions plus the latest CUDA release.
+
 Quick Start
 ^^^^^^^^^^^