Add info on freesurfer requirement for bare install to address #1034

[neurorepro]

No description provided.

[celprov]

I don't know why this PR triggers a change in IQMs computation?! This is really strange
@oesteban @esavary any insight? Can we merge nonetheless?

[effigies]

CircleCI is failing for everything. This PR does not need to be held up on a general problem.

[welcome]

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