contribution guidelines updates - contentType instance library

[lzehl]

• minimum contribution: name with short description or link to specification
• define naming convention for name (based IANA logic)
  • cf. discussion in revision of content type naming convention openMINDS_instances#320
  • <primary-type>/vnd.<vendor>.<format>-v<version>-b<bitness>[-<role>]+<suffix>
  • current and potential primary-types: application, audio, image, model, text, video, chemical (?)
  • current and potential suffixes: +binary, +json, +tsv, +csv, +xml, +yaml, +zip, +gzip, +mat, +hdf5, +hdf, +h5, +n5, +python, +ms-excel, +txt, +fastq, +txt, +plain, +dzi, +dzip, +hoc
• use definingSource to point to the exact external definition (IANA or mimetype.io)
• use isBasedOn to infer "parent" openMINDS ContentType