[DOC] Developers section

[oesteban]

Open a new section in the documentation, that shows the guidelines and principles to contribute to fMRIPREP, and also gives finer detail on technical aspects of fmriprep.

In particular, and following @TimVanMourik's open review comment (http://preprint.space/openreviewers/0000-0002-8155-8641), fMRIPrep should describe its primarily features more clearly and in detail:

• Automatic data type recognition
• Rich support of data types
• Rich visual performance feedback
• Increased performance by best-in-breed approach.

[emdupre]

It seems that this would, at least in part, overlap with the Contributing to fMRIPrep section of the documentation, no?

[oesteban]

Yep, this would extend that section with more theoretical issues.

[oesteban]

I think this should be addressed now more generally in the nipreps documentation - moving there.