docs: update READM file

README.md

@@ -62,7 +62,7 @@ mask_img.save("thumbnail_mask.png")
 
 ## Preparing the Thumbnail
 
-AtlasPatch generates thumbnails at **1.25× objective power** (power-based downsampling) and then clamps the longest side to **1024 px**. Using the same helper the library uses:
+AtlasPatch generates thumbnails at **1.25× objective power** (power-based downsampling) and then resizes to **1024x1024 px**
 
 ```python
 from atlas_patch.core.wsi import WSIFactory