Add n of kpts in zebra data

metadata.yaml

@@ -567,7 +567,7 @@ SLEAP_OSFM_zebras_drone.h5:
     file_name: null
     sha256sum: null
   note: 44 trajectories of zebras (Equus quagga) in escape behaviour, in world coordinate
-    system, recorded for 3.5 min. The original trajectory data was obtained from a moving camera drone,
-    and then expressed in a coordinate system fixed to the ground using structure-from-motion
-    (with OpenSFM and OpenDroneMap). See https://github.com/neuroinformatics-unit/zebras-stitching
-    for further details.
+    system, recorded for 3.5 min. Each individual has two keypoints: head and tail. The 
+    original trajectory data was obtained from a moving camera drone, and then expressed in 
+    a coordinate system fixed to the ground using structure-from-motion (with OpenSFM and OpenDroneMap). 
+    See https://github.com/neuroinformatics-unit/zebras-stitching for further details.