Document purpose of studyspec fields

[mih]

Please edit, what are possible values (if there are limited choices), what is it used for:

• anon_subject anonymized subject ID. To be used for conversion if spec2bids is called with --anonymize
• bids_modality modality according to BIDS. To be used for conversion and therefore for the naming scheme of converted files
• bids_run run according to BIDS. To be used for conversion and therefore for the naming scheme of converted files
• bids_session session according to BIDS. To be used for conversion and therefore for the naming scheme of converted files
• bids_task task according to BIDS. To be used for conversion and therefore for the naming scheme of converted files
• comment free to use. Intended to ease maintenance and specification editing by humans
• converter converter to be used. ATM just either heudiconv or ignore (to not convert at all)
• dataset_id datalad dataset ID of the (DICOM-)dataset
• dataset_refcommit commit of the (DICOM-) dataset this specification is referring to
• description human readable description of the image series
• id human readable id of the image series. Defaults to SeriesNumber from DICOM metadata
• location location of the DICOMs containing this image series
• status unused ATM
• subject subject ID. Either specified by the user or guessed from DICOM metadata. This is the non-anonymized subject ID
• type type of the data this specification is about. Kind of specification class. Most important ATM is dicomseries, which denominates a specification of a DICOM image series
• uid unique identifier of an image series. This is the SeriesInstanceUID from DICOM headers. Used during conversion by spec2bids to match image series data as found by heudiconv with this specification

[mih]

This is done.