Add warning when using activation mixed precision (#1182)

* Add warning when using activation mixed precision

model_compression_toolkit/core/runner.py

@@ -152,6 +152,12 @@ def core_runner(in_model: Any,
                 f'Mixed Precision has overwrite bit-width configuration{core_config.mixed_precision_config.configuration_overwrite}')
             bit_widths_config = core_config.mixed_precision_config.configuration_overwrite
 
+        if (target_resource_utilization.activation_memory < np.inf or
+                target_resource_utilization.total_memory < np.inf):
+            Logger.warning(
+                f"Running mixed precision for activation compression, please note this feature is experimental and is "
+                f"subject to future changes. If you encounter an issue, please open an issue in our GitHub "
+                f"project https://github.com/sony/model_optimization")
     else:
         bit_widths_config = []