Documentation update

[larmi01-itq]

file: README.md section: Setup step: 5a

I got an error with the following command: aws lambda invoke
--function-name $CFN_STACK_NAME-UpdateWAFIPSets
--region $REGION
--payload file://lambda/test_event.json lambda_return.json error: An error occurred (InvalidRequestContentException) when calling the Invoke operation: Could not parse request body into json: Could not parse payload into json: Invalid UTF-8 middle byte 0x28"

I had to add the parameter --cli-binary-format raw-in-base64-out since the input is not base64 encoded.

Thanks for the sample very helpful.