add challenge dataset

.gitattributes

@@ -28,3 +28,4 @@ saved_model/**/* filter=lfs diff=lfs merge=lfs -text
 test.json filter=lfs diff=lfs merge=lfs -text
 train.json filter=lfs diff=lfs merge=lfs -text
 validation.json filter=lfs diff=lfs merge=lfs -text
+challenge_woSectionHeader.json filter=lfs diff=lfs merge=lfs -text