[ENH] Allow README file extensions.

[mateuszpawlik]

Closes #972

Tasks to complete:

• Modify the README description in documentation https://github.com/bids-standard/bids-specification/blob/master/src/03-modality-agnostic-files.md#readme
• Modify the description in the schema

  bids-specification/src/schema/objects/top_level_files.yaml

  Lines 24 to 26 in ba11771

  	In addition a free form text file (`README`) describing the dataset in more details SHOULD be
  	provided.
  	The `README` file MUST be either in ASCII or UTF-8 encoding.

• Add new file extensions

  bids-specification/src/schema/rules/top_level_files.yaml

  Line 5 in ba11771

  - None

• Allow file extensions for README bids-validator#1431 - I think the validator should be updated before the specification changes are merged in. (PR here: Allow .md .txt or .rst for README bids-validator#1432)

I kept the README description in the specification and in the schema equal. Maybe a macro could help not to need to update such definitions in two places.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.50%. Comparing base (4a6c49a) to head (815c62e).
Report is 1460 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #1033       +/-   ##
===========================================
+ Coverage   34.05%   71.50%   +37.45%     
===========================================
  Files           8        9        +1     
  Lines         834      930       +96     
===========================================
+ Hits          284      665      +381     
+ Misses        550      265      -285     

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[sappelhoff]

another open question is whether we should allow these extension also for the LICENSE and CHANGES files.

given that CHANGES must follow CPAN convention, only .txt may make sense as an extension.

Furthermore I don't know any license in MD or RST syntax, so here again .txt might be the only meaningful extension near to the existing "no extension" convention.

WDYT?

[tsalo]

I agree that we probably shouldn't update LICENSE or CHANGES given that they are more restrictive than README. If someone requests them in the future, we can revisit.

[Remi-Gau]

I agree that we probably shouldn't update LICENSE or CHANGES given that they are more restrictive than README. If someone requests them in the future, we can revisit.

I 1000% agree with this

[yarikoptic]

mostly just non-consequential comments, with one concern -- why not to restrict .md to basic? I bet openneuro and other portals would prefer to render those .md files. If flavor is not regulated -- it would cause troubles, thus reducing the benefit from having .md to start with.

[sappelhoff]

before I forget it @mateuszpawlik could you please add yourself to the contributors list here? https://github.com/bids-standard/bids-specification/wiki/Recent-Contributors

We sync that wiki entry with the corresponding page in the BIDS specification before every new release.

[sappelhoff]

Thanks for this contribution @mateuszpawlik!

[mateuszpawlik]

Thank you all for making it happen. That was a nice experience :-) I'm looking forward to more.