update docstring of vp-upload to reflect new functionality

validphys2/src/validphys/scripts/vp_upload.py

 """
-Upload a resource (but not a fit) to the NNPDF server. By default this uploads
-a validphys report to the server. For that use `vp-upload <output folder>`.
-NB: to upload a fit, use the separate script `vp-uploadfit`.
+Upload a resource to the NNPDF server.
+
+The script automatically detects (:py:func:`validphys.uploadutils.check_input`)
+the type of the input.
+
+ - A ``fit`` is defined to be any folder structure that contains a ``filter.yml``
+   file at its root
+ - a ``PDF`` is any folder containing a ``.info`` file at the root and a replica 0
+ - a report is any such structure containing an ``index.html`` file at the root.
+
+The input folder is then placed in the correct location in the server accordingly.
+
 """
 #Note that the imports are done as late as possible to improve the speed of
 #the command line.