docs: 🐛 use absolute logo URL so PyPI renders it (#41)

PyPI can't resolve the relative docs/assets/logo.png path, so the project
page showed the alt text instead of the image. Point the README <img> at
the raw.githubusercontent.com URL (works on GitHub and PyPI).

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: lguerard

README.md

@@ -1,5 +1,5 @@
 <p align="center">
-  <img src="docs/assets/logo.png" alt="patchworks logo" width="220">
+  <img src="https://raw.githubusercontent.com/imcf/patchworks/main/docs/assets/logo.png" alt="patchworks logo" width="220">
 </p>
 
 # patchworks