Add experimental warning to docs.

Summary: TF2.4 Only

Reviewers: #tensorflow, #framework_ip_review_-_any_oss_or_third-party_code_use_has_been_approved, georgep

Reviewed By: #tensorflow, #framework_ip_review_-_any_oss_or_third-party_code_use_has_been_approved, georgep

Maniphest Tasks: T41177

Differential Revision: https://phabricator.sourcevertex.net/D53355

Author: JackHunt

tensorflow/python/ipu/keras/optimizers/automatic_loss_scaling_optimizer.py

@@ -27,7 +27,9 @@
 
 
 class AutomaticLossScalingOptimizer(IpuOptimizer):
-  """An optimizer that automatically computes and applies
+  """EXPERIMENTAL - DO NOT USE
+
+  An optimizer that automatically computes and applies
   a loss scaling factor (LSF) prior to gradient computation.
 
   The LSF is computed such that the magnitude of the loss is increased

tensorflow/python/ipu/optimizers/automatic_loss_scaling_optimizer.py

@@ -40,7 +40,9 @@ def __init__(self,
                accumulate_statistics_over_update_period=True,
                ratio_threshold=10e-6,
                name="AutomaticLossScalingOptimizer"):
-    """ Construct an AutomaticLossScalingOptimizer.
+    """EXPERIMENTAL - DO NOT USE
+
+    Construct an AutomaticLossScalingOptimizer.
 
     Args:
       wrapped_optimizer: TensorFlow (derived) optimizer.