Update README.md

Author: thibaud-perrin

README.md

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 **Deploy your own private PyPI-compatible package registry on Railway in under 2 minutes.**
 Based on [devpi](https://devpi.net), with persistent storage and full compatibility with `pip`, `uv`, and `twine`.
 
-[![Deploy on Railway](https://railway.com/button.svg)](https://railway.com/new/template)
+[![Deploy on Railway](https://railway.com/button.svg)](https://railway.com/deploy/4_qIAt?referralCode=0fPTYP&utm_medium=integration&utm_source=template&utm_campaign=generic)
 
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