v0.12.1

🐛 Bug Fix

• Re-add explicit instructions to install dcm2niix "manually" and remove it from install_requires #651 (@yarikoptic)

📝 Documentation

• Contributing guide. #641 (@TheChymera)
• Reword and correct punctuation on installation.rst #643 (@yarikoptic @candleindark)

Authors: 3

• Horea Christian (@TheChymera)
• Isaac To (@candleindark)
• Yaroslav Halchenko (@yarikoptic)