Update README.md with information about openshift-registry

[chmouel]

Updating README with information on how to use openshift internal registry with ko.

[imjasonh]

Thanks for adding this! 👍

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[codecov-commenter]

Codecov Report

Merging #346 (d2fb66f) into main (29cd8e0) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #346   +/-   ##
=======================================
  Coverage   38.37%   38.37%           
=======================================
  Files          33       33           
  Lines        1522     1522           
=======================================
  Hits          584      584           
  Misses        844      844           
  Partials       94       94           

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