update README with shape of test image

README.md

@@ -63,7 +63,7 @@ ds = dataset.with_format("np")
 Now you should be able to use the `ds` variable like:
 
 ```python
-ds["test"][0]["image"].shape # -> (TBD)
+ds["test"][0]["image"].shape # -> (9, 2048, 2048)
 ```
 
 Note of course that it will take a long time to download and convert the images in the local cache for the `full` dataset. Afterward, the usage should be quick as the files are memory-mapped from disk.