replaced cnn link with arxiv

docs/source/index.rst

@@ -2,7 +2,7 @@
 Flow Matching
 =============
 
-`flow_matching` is a PyTorch library for implementing flow matching algorithms, featuring state-of-the-art continuous and discrete implementations. It includes practical examples for both text and image modalities. This repository is part of `Flow Matching Guide and Codebase <http://cnn.com>`_.
+`flow_matching` is a PyTorch library for implementing flow matching algorithms, featuring state-of-the-art continuous and discrete implementations. It includes practical examples for both text and image modalities. This repository is part of `Flow Matching Guide and Codebase <https://arxiv.org/abs/2412.06264>`_.
 
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