add a build-and-test status badge to the README (#33)

Summary: Pull Request resolved: #33

Test Plan: {F1285880687}

Reviewed By: dtolnay

Differential Revision: D52731085

Pulled By: shayne-fletcher

fbshipit-source-id: 8101b7c88b26dccbd5d1433b396a22b289af19e5

README.md

@@ -1,4 +1,4 @@
-# Reindeer - Building Cargo Packages with Buck
+# Reindeer - Building Cargo Packages with Buck [![Build Status](https://github.com/facebookincubator/reindeer/actions/workflows/build-and-test.yml/badge.svg)](https://github.com/facebookincubator/reindeer/actions)
 
 Jeremy Fitzhardinge <[email protected]>