warning on documentation re-use

[pbellec]

We should warn users we want them to use the docs unchanged, to the greatest extent possible. Something akin to what fmriprep has:

The technical documentation was generated by the Courtois NeuroMod team with the express intention that users should copy and paste this text into their manuscripts unchanged. It is released under the CC0 license. All references in the text link to a .bib file with detailed reference list, ready to be incorporated in a LaTeX document.