Update tutorial to indicate naming requirements

[Connor-Bowley]

The tutorial linked to in SlicerSALT does not make clear the file naming requirements enforced by the following code. Update the tutorial accordingly:

GROUPS/Modules/Scripted/RigidAlignmentModule/RigidAlignmentModule.py

Lines 101 to 103 in 71daa95

	models = self.inputDir.glob('*_pp_surf_SPHARM.vtk')
	fiducials = self.fiducialsDir.glob('*_fid.fcsv')
	unitSphere = next(self.commonSphereDir.glob('*_surf_para.vtk'))