Update MLIR generate-test-checks.py to add the notice from the source into the generated file

[mehdi_amini]

Summary

Folks may not read the source of the tool and miss these instructions.

[rriddle]

Nice, thanks!

[jpienaar]

Thanks

mlir/utils/generate-test-checks.py

 # See https://llvm.org/LICENSE.txt for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 import argparse
 import os  # Used to advertise this file's name ("autogenerated_note").
 import re
 import sys
 
-ADVERT = '// NOTE: Assertions have been autogenerated by '
+ADVERT_BEGIN = '// NOTE: Assertions have been autogenerated by '
+ADVERT_END = """
+// The script is designed to make adding checks to
+// a test case fast, it is *not* designed to be authoritative
+// about what constitutes a good test! The CHECK should be
+// minimized and named to reflect the test intent.
+"""
+
 
 # Regex command to match an SSA identifier.
 SSA_RE_STR = '[0-9]+|[a-zA-Z$._-][a-zA-Z0-9$._-]*'
 SSA_RE = re.compile(SSA_RE_STR)
 
 
 # Class used to generate and manage string substitution blocks for SSA value
 # names.
def main():
   args = parser.parse_args()
 
   # Open the given input file.
   input_lines = [l.rstrip() for l in args.input]
   args.input.close()
 
   # Generate a note used for the generated check file.
   script_name = os.path.basename(__file__)
-  autogenerated_note = (ADVERT + 'utils/' + script_name)
+  autogenerated_note = (ADVERT_BEGIN + 'utils/' + script_name + "\n" + ADVERT_END)
 
   source_segments = None
   if args.source:
     source_segments = process_source_lines(
         [l.rstrip() for l in open(args.source, 'r')],
         autogenerated_note,
         args
     )