Fix a link to openneuro-cli

[yarikoptic]

I also tried to find other possibly broken links using https://github.com/scivision/linkchecker-markdown
but it pointed only to another which is ok but 400:

❯ python -m linkcheckmd docs/

 ('api.md', 'https://openneuro.org/crn/graphql', 400)

so should be all good

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2d9d6c0) 65.15% compared to head (ec39c4b) 65.15%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2989   +/-   ##
=======================================
  Coverage   65.15%   65.15%           
=======================================
  Files         380      380           
  Lines       24487    24487           
  Branches      878      878           
=======================================
  Hits        15954    15954           
  Misses       8533     8533           

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