add spec violation note in the tutorial (#1116)

Summary:
Pull Request resolved: #1116

More clear guidance given the reported issue: #1062

Reviewed By: mergennachin

Differential Revision: D50561885

fbshipit-source-id: 10b2a5706595aa411d70d314f06223790588fe90

Author: cccclai

docs/source/tutorials_source/export-to-executorch-tutorial.py

@@ -351,6 +351,11 @@ def call_operator(self, op, args, kwargs, meta):
 print("Transformed Edge Dialect Graph")
 print(transformed_edge_program.exported_program())
 
+######################################################################
+# Note: if you see error like `torch._export.verifier.SpecViolationError: Operator torch._ops.aten._native_batch_norm_legit_functional.default is not Aten Canonical`,
+# please file an issue in https://github.com/pytorch/executorch/issues and we're happy to help!
+
+
 ######################################################################
 # Delegating to a Backend
 # -----------------------