Add missing comment about TPU disable to multi_process_runner.

PiperOrigin-RevId: 337897956
Change-Id: Ica51a636eecbcc426c1c1c02253ccc1e6068867c
diff --git a/tensorflow/python/distribute/multi_process_lib.py b/tensorflow/python/distribute/multi_process_lib.py
index e733d6b..d194ac1 100644
--- a/tensorflow/python/distribute/multi_process_lib.py
+++ b/tensorflow/python/distribute/multi_process_lib.py
@@ -32,6 +32,8 @@
 
 
 def _is_enabled():
+  # Note that flags may not be parsed at this point and simply importing the
+  # flags module causes a variety of unusual errors.
   tpu_args = [arg for arg in sys.argv if arg.startswith('--tpu')]
   if is_oss() and tpu_args:
     return False