add custom user pool example

Author: DavidWells

README.md

@@ -105,6 +105,7 @@ serverless install -u https://github.com/author/project -n my-project
 | Example | Author |
 |:-------|:------:|
 | **[Aws Api Gateway Serverless Project Written In Go](https://github.com/yunspace/serverless-golang)** <br/> A serverless project that contains an API Gateway endpoint powered by a Lambda function written in golang and built using [eawsy/aws-lambda-go-shim](https://github.com/eawsy/aws-lambda-go-shim). | [yunspace](http://github.com/yunspace) |
+| **[Aws Cognito Custom User Pool Example](https://github.com/bsdkurt/aws-node-custom-user-pool)** <br/> Example CloudFormation custom resource backed by a lambda using Cognito User Pools | [bsdkurt](http://github.com/bsdkurt) |
 | **[Aws Lambda Power Tuning (Powered By Step Functions)](https://github.com/alexcasalboni/aws-lambda-power-tuning)** <br/> Build a [Step Functions](https://aws.amazon.com/step-functions/) state machine to optimize your AWS Lambda Function memory/power configuration. | [alexcasalboni](http://github.com/alexcasalboni) |
 | **[Amazon Kinesis Streams Fan Out Via Kinesis Analytics](https://github.com/alexcasalboni/kinesis-streams-fan-out-kinesis-analytics)** <br/> Use [Amazon Kinesis Analytics](https://aws.amazon.com/kinesis/analytics/) to fan-out your Kinesis Streams and avoid read throttling. | [alexcasalboni](http://github.com/alexcasalboni) |
 | **[Open Bot](https://github.com/open-bot/open-bot)** <br/> An unoptionated Github bot driven by a configuration file in the repository | [open-bot](http://github.com/open-bot) |