[MLIR] NFC: improve comment about MLIR_CMAKE_DIR.

Author: chsigg

mlir/test/CMakeLists.txt

@@ -5,8 +5,8 @@ if (MLIR_ENABLE_BINDINGS_PYTHON)
   add_subdirectory(python)
 endif()
 
-# Passed to lit.site.cfg.py.so that the out of tree Standalone dialect test
-# can find MLIR's CMake configuration
+# Provide the MLIR CMake module dir so that the out of tree Standalone
+# dialect and can add it to the module path.
 set(MLIR_CMAKE_DIR
   "${CMAKE_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX}/cmake/mlir")