Add download instructions for FTP CLI client.

[mkcor]

Hi @dominikl,

I thought I would document how to download IDR data with ftp at the command line, so that my experience could benefit others.

This is a follow-up to:

• https://github.com/IDR/idr.openmicroscopy.org/pull/193#issue-2258303892
• https://forum.image.sc/t/permission-denied-when-trying-to-download-idr-openmicroscopy-at-fasp/88907/3

[dominikl]

Thank you very much, that's a good idea. Could you please provide a "contributor license agreement", see https://ome-contributing.readthedocs.io/en/latest/cla.html . As this is a bit more than just a little typo fix, I think we might actually need a CLA before being able to merge the PR.

[mkcor]

Ok, done!

[pwalczysko]

lgtm thank you @mkcor