feat(readme): update the readme to include NAT (#163)

README.md

@@ -4,6 +4,7 @@ This repository is an extension of the [Optimism monorepo](https://github.com/et
 
 ## Components
 - op-conductor-mon: Monitors multiple op-conductor instances and provides a unified interface for reporting metrics.
+- op-nat: Network Acceptance Tester: A tool that tests the network acceptance of devnets. (See [op-nat/README.md](./op-nat/README.md) or [devdocs/pm](https://devdocs.optimism.io/pm/acceptance-testing.html) for more information)
 - op-signer: Thin gateway that supports various RPC endpoints to sign payloads from op-stack components using private key stored in KMS.
 - op-ufm: User facing monitoring creates transactions at regular intervals and observe transaction propagation across different RPC providers.