[DOC] add guides in eg walkthrough: if there is no internet on compute nodes

[zhao-cy]

It seems like some clusters do not have internet connection on compute nodes. e.g., see issue #118 reported by @yibeichan. Therefore, users should get all data content of the input datasets before submitting the jobs.

[zhao-cy]

@yibeichan I've updated the example walkthrough by adding several drop-down boxes called If there is no Internet connection on compute nodes - see the update example walkthrough here - note: this doc is built upon a branch, not the main branch, so the link is different from the one you usually use.

If you have time, could I ask you a favor of going thru this example walkthrough on Princeton cluster, and see if this works now? I hope to make sure it's working on clusters w/o internet connections on compute node. I've tried the added commands, but the clusters I have access to all have internets, so hope to double check in the real scenario w/o internet. Would greatly appreciate it if you do so!

[zhao-cy]

Yibei has confirmed that what I instructed in issue #118 worked on Princeton neuroscience institute cluster - she can successfully go thru the entire example walkthrough all the way to the end, i.e., all 6 jobs successfully finished + branches were merged, and finally get the correct number from sub-01, ses-A.

[zhao-cy]

I am merging this to main now. Instructions to be added in other parts of the docs will be done when completing issue #115.

[zhao-cy]

Oops, I forgot to add one minor notes in the example walkthrough. As I already merged this branch to main, I'll directly added it in the main branch.

(after datalad get *:)

You should see these printed messages from ``datalad`` at the end:

    .. code-block:: console

        action summary:
          get (notneeded: 1, ok: 47)