[ENH] Add explicit wording on DICOM terms correspondence (#1450)

* Add explicit wording on DICOM terms correspondence

* Extend to Based on for DICOM

* Update src/common-principles.md

Co-authored-by: Stefan Appelhoff <stefan.appelhoff@mailbox.org>

* Update avoiding "instructions to spec authors" language

Co-authored-by: Chris Markiewicz <effigies@gmail.com>

---------

Co-authored-by: Remi Gau <remi_gau@hotmail.com>
Co-authored-by: Stefan Appelhoff <stefan.appelhoff@mailbox.org>
Co-authored-by: Chris Markiewicz <effigies@gmail.com>

src/common-principles.md

@@ -449,6 +449,11 @@ possible. Since the NIfTI standard offers limited support for the various image
 acquisition parameters available in DICOM files, we RECOMMEND that users provide
 additional meta information extracted from DICOM files in a sidecar JSON file
 (with the same filename as the `.nii[.gz]` file, but with a `.json` extension).
+Currently defined metadata fields are listed in the [Glossary](./glossary.md).
+Where possible, DICOM Tags are adopted directly as BIDS metadata terms and
+indicated with "**Corresponds to** DICOM Tag ID1, ID2 `DICOM Tag Name`.".
+When harmonization has been deemed necessary, this is indicated in the
+BIDS term description with "**Based on** DICOM Tag ID1, ID2 `DICOM Tag Name`.".
 Extraction of BIDS compatible metadata can be performed using [dcm2niix](https://github.com/rordenlab/dcm2niix)
 and [dicm2nii](https://www.mathworks.com/matlabcentral/fileexchange/42997-xiangruili-dicm2nii)
 DICOM to NIfTI converters. The [BIDS-validator](https://github.com/bids-standard/bids-validator)