Update coverage map image link in README

Author: FrankFeng-23

README.md

@@ -11,7 +11,7 @@ representation maps at 10m resolution. These embeddings compress a full year of
 temporal-spectral features into dense representations optimized for downstream
 geospatial analysis tasks. Read more details about [the model](https://github.com/ucam-eo/tessera).
 
-![Coverage map](https://raw.githubusercontent.com/ucam-eo/tessera-coverage-map/refs/heads/main/map.png)
+![Coverage map](https://github.com/ucam-eo/tessera-coverage-map/blob/main/tessera_coverage.png)
 
 ### Request missing embeddings