message: Fixed issue which caused SimpleRTK to fail to compile
  because ITK/README.txt file has been renamed to ITK/README.md after v4.12.2
diff: @@ -330,17 +330,23 @@ get_filename_component( _itk_root "${_itk_root}" PATH )
  get_filename_component( _itk_root "${_itk_root}" PATH )
  set( _itk_doc_path "${_itk_root}/share/doc/ITK-${ITK_VERSION_MAJOR}.${ITK_VERSION_MINOR}" )
  +if(ITK_VERSION VERSION_LESS "4.12.2")
  + set(_readme "README.txt")
  +else()
  + set(_readme "README.md")
  +endif()
  +
  if( EXISTS "${_itk_source_path}/NOTICE" )
  set( ITK_DOC_FILES
  # "${_itk_source_path}/LICENSE" SimpleRTK has same license file
  "${_itk_source_path}/NOTICE"
  - "${_itk_source_path}/README.txt"
  + "${_itk_source_path}/${_readme}"
  )
  elseif( EXISTS "${_itk_doc_path}/NOTICE" )
  set( ITK_DOC_FILES
  # "${_itk_doc_path}/LICENSE" SimpleRTK has same license file
  "${_itk_doc_path}/NOTICE"
  - "${_itk_doc_path}/README.txt"
  + "${_itk_doc_path}/${_readme}"
  )
  else()
  message( "doc_path: ${_itk_doc_path}" )
  