Updated README with missing step to aggregate votes.

Author: jbnunn

README.md

@@ -35,9 +35,11 @@ Step 2 – Visit the [API Gateway dashboard](https://console.aws.amazon.com/apig
 
 Under `Body Mapping Templates`, set the "Content-Type" to `application/x-www-form-urlencoded`, and add [this mapping template](apigateway-mappingtemplate.txt).
 
-Step 3 – Visit the [Amazon Cognito dashboard](https://console.aws.amazon.com/cognito/home) and create a new identity pool that allows access to unauthenticated identities. Modify the policy document to allow read access to the aggregates DynamoDB table created by the AWS CloudFormation script above. This allows unauthenticated users to retrieve data from the vote aggregation table in DynamoDB. Amazon Cognito will provide sample code for the JavaScript platform. Note the value for identity pool ID; you'll need it in step 4.
+Step 3 – Visit the [Amazon Cognito dashboard](https://console.aws.amazon.com/cognito/home) and create a new identity pool that allows access to unauthenticated identities. Modify the policy document to allow read access to the aggregates DynamoDB table created by the AWS CloudFormation script above. This allows unauthenticated users to retrieve data from the vote aggregation table in DynamoDB. Amazon Cognito will provide sample code for the JavaScript platform. Note the value for identity pool ID; you'll need it in step 5.
 
-Step 4 – Copy the HTML, CSS, and JS files from this repo and into the static S3 bucket that was created to hold your dashboard. You'll need to open `refresh.js` and replace default values of `region` and `identity-pool-id` with your own values.
+Step 4 – In the __VoteApp__ table in DynamoDB, create a new [Trigger](https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Streams.Lambda.html), and point it to the existing Lambda function to [aggregate votes](lambda-functions/aggregate-votes/app.js). This function will monitor any changes to your __VoteApp__ table, writing new, aggregate values into __VoteAppAggregates__.
+
+Step 5 – Copy the HTML, CSS, and JS files from this repo and into the static S3 bucket that was created to hold your dashboard. You'll need to open `refresh.js` and replace default values of `region` and `identity-pool-id` with your own values.
 
 Congratulations! You now should have a working example of the reference architecture. You are able to receive votes in real time, tune your DynamoDB table to handle various levels of incoming traffic, and watch your results change on your dashboard in real time!