Add orthogonalized motion components to confounds file

[tsalo]

Closes #52.

Changes proposed in this pull request

• Rename unstable to main in documentation.
• Add columns named aroma_orth_motion_ to confounds file.
• Rename confounds file from desc-melodic to desc-aroma.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 13 lines in your changes missing coverage. Please review.

Project coverage is 31.38%. Comparing base (8e0fc45) to head (fac6dae).
Report is 21 commits behind head on main.

Files with missing lines	Patch %	Lines
src/fmripost_aroma/interfaces/confounds.py	0.00%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #56      +/-   ##
==========================================
- Coverage   31.55%   31.38%   -0.17%     
==========================================
  Files          26       26              
  Lines        2266     2278      +12     
  Branches      359      360       +1     
==========================================
  Hits          715      715              
- Misses       1530     1542      +12     
  Partials       21       21              

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