Update README.md

Author: EauDeData

README.md

@@ -11,9 +11,13 @@ The file `train_set_labels.json` maps authors to their books and pages:
 ```json
 {
   "AuthorID_1": {
-      "BookID_A": ["page_0001", "page_0002", ...],
-      "BookID_B": ["page_0101", "page_0102", ...]
+      "BookID_A": ["page_0001.png", "page_0002.png"],
+      "BookID_B": ["page_0101.png", "page_0102.png"]
   },
-  "AuthorID_2": { ... },
-  ...
+  "AuthorID_2": { },
 }
+
+```
+Where the path to the documents are organized as follows: `/<root_folder>/BOOK_ID/PAGE_ID.png`. 
+In the intra-book tasks, authors will receive a set of queries QUERY_ID and are expected to return a similarity per PAGE_ID in the training set; where QUERY_ID and PAGE_ID are expected to be from the same book. 
+In book-level retrieval, authors will receive a set of query books BOOK_QUERY_ID (multi-page) and are expected to return a similarity per BOOK_ID_N in the training set; where BOOK_QUERY_ID and BOOK_ID_N are expected to be from the same author.