Add the black style badge

[chkoar]

Reference Issue

What does this implement/fix? Explain your changes.

Any other comments?

[codecov]

Codecov Report

Merging #799 (9d5672b) into master (72d939a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #799   +/-   ##
=======================================
  Coverage   98.58%   98.58%           
=======================================
  Files          87       87           
  Lines        5736     5736           
  Branches      479      479           
=======================================
  Hits         5655     5655           
  Misses         80       80           
  Partials        1        1           

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[glemaitre]

Thanks.