Added a link to Postman collection under Tools

build/tools/README.md

@@ -4,5 +4,7 @@
 
 [**Avash**](avash.md)**:** is a shell client for interacting with Avalanche and can deploy local networks and interact with the nodes in those networks. You can use Avash to rapidly launch test network environments.
 
-[**Ortelius API**](ortelius.md): is an API that allows clients to interact with Ortelius, the Avalanche indexer.
+[**Ortelius API**](ortelius.md)**:** is an API that allows clients to interact with Ortelius, the Avalanche indexer.
+
+[**Postman collection**](https://github.com/ava-labs/avalanche-postman-collection)**:** is an AvalancheGo API template and environment collection for [Postman](https://postman.com/), a tool to simplify API development and experimentation. The collection covers all of AvalancheGo APIs, so you can easily issue commands to your node and examine the output in a nicely formatted, readable way.