message: add explanation for is_runtime_ext_enabled API
diff: @@ -76,7 +76,9 @@ def is_runtime_ext_enabled():
  None (None): None
  Returns:
  - bool: Whether the runtime exetension is enabled or not.
  + bool: Whether the runtime exetension is enabled or not. If the
  + Intel OpenMP Library is preloaded, this API will return True.
  + Otherwise, it will return False.
  """
  return ipex._C.is_runtime_ext_enabled() == 1
  