force removes the reference diffusion measures

[tashrifbillah]

Add a note in README.md

https://github.com/pnlbwh/dMRIharmonization/blob/spm-bspline/lib/harmonization.py#L268

The above checking is there to let a user harmonize data multiple times without having to remove previous results manually.

Make a note about --force in general.

[tashrifbillah]

If all cases are copied to one directory and dti directory is same for all cases, the above happens.

Ideally, each case should have its own folder, the problem won't happen.

[tashrifbillah]

When you want to --debug under the above condition, reference diffusion measures are no longer there and so --debug fails.

[tashrifbillah]

Prompt the user to have separate directories for each case or NOT use --debug.