Added a section about SCALATEST_RUN_FLICKER_TESTS in README.md.
Added a section about SCALATEST_RUN_FLICKER_TESTS in README.md.

cheeseng/scalatest,cheeseng/scalatest,dotty-staging/scalatest,dotty-staging/scalatest,scalatest/scalatest,dotty-staging/scalatest,scalatest/scalatest,cheeseng/scalatest,scalatest/scalatest