Document the transforms produced by QSIPrep

[tsalo]

Closes none.

Changes proposed in this pull request

• Document the transforms written out by QSIPrep, including anat-to-ACPC and ACPC-to-template.
• Document the transforms not currently written out by QSIPrep, including the motion+eddy+SDC transform and the dwiref-to-ACPC transform.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 28.54%. Comparing base (ea25085) to head (cbe90ce). Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #866 +/- ## ======================================= Coverage 28.54% 28.54% ======================================= Files 68 68 Lines 10135 10135 Branches 1140 1140 ======================================= Hits 2893 2893 Misses 7143 7143 Partials 99 99 ```

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