Doc/catalog image duration (#1172)

GitOrigin-RevId: aa452eb20338fa030299dbffcab4d77db47d51f8

Author: hangdl

descarteslabs/client/services/catalog/catalog.py

@@ -545,7 +545,7 @@ def add_image(self, product_id, image_id, add_namespace=True, **kwargs):
         :param float degraded_fraction_0:
         :param str descartes_version:
         :param str directory: Subdirectory location.
-        :param float duration:
+        :param float duration: duration of the scan in seconds
         :param int duration_days:
         :param float earth_sun_distance: Earth sun distance at time of image capture.
         :param list(str) files: Names of the files this image is stored in.