Adding Dixa to adopters in README

[jospint]

Employed at Dixa, we have been using Scala Steward for a few years

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.83%. Comparing base (cd2974c) to head (fee6643).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3619   +/-   ##
=======================================
  Coverage   89.83%   89.83%           
=======================================
  Files         174      174           
  Lines        5045     5045           
  Branches      488      488           
=======================================
  Hits         4532     4532           
  Misses        513      513           

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