Update README.md (#819)

Author: sashaphmn

README.md

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 # Wormhole TypeScript SDK
 
+[![GitHub build](https://github.com/wormhole-foundation/wormhole-sdk-ts/actions/workflows/build.yml/badge.svg)](https://github.com/wormhole-foundation/wormhole-sdk-ts/actions)
 [![npm version](https://img.shields.io/npm/v/@wormhole-foundation/sdk.svg)](https://www.npmjs.com/package/@wormhole-foundation/sdk)
 
 The Wormhole Typescript SDK is useful for interacting with the chains Wormhole supports and the [protocols](#protocols) built on top of Wormhole.