message: Add changelog and readme to install
  This changelist adds two root-level documents, CHANGELOG.md and README.md, to installations of MaterialX.
diff: @@ -181,6 +181,10 @@ if(${CMAKE_VERSION} VERSION_GREATER "3.6.2")
  endif()
  endif()
  +# Install root-level documents
  +install(FILES CHANGELOG.md README.md
  + DESTINATION ${CMAKE_INSTALL_PREFIX})
  +
  include(CMakePackageConfigHelpers)
  write_basic_package_version_file(${CMAKE_BINARY_DIR}/cmake/MaterialXConfigVersion.cmake
  VERSION ${CMAKE_VERSION}
  