update download instructions to use idc-index

[fedorov]

No description provided.

[fedorov]

@s-paquette can you also please update the manifest generation part to have the following for the header:

# To download the files in this manifest, first install idc-index python 
# package (https://github.com/ImagingDataCommons/idc-index),
# then run the following command:
#
#   idc download manifest.s5cmd
#
# See IDC documentation for more details: https://learn.canceridc.dev/data/downloading-data
#

[fedorov]

Right now, as discovered by @bcli4d, the revised instructions will not allow download of items from the previous data versions of IDC, that are not available in the current version, which is a regression relative to the pure s5cmd-based approach. It is probably better to wait for the resolution of ImagingDataCommons/idc-index#100 before this is merged.