docs: add CI badge to README

Author: fcladera

README.md

@@ -1,5 +1,8 @@
 ☕ MOCHA: Multi-robot Opportunistic Communication for Heterogeneous Collaboration
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+
+[![build](https://github.com/KumarRobotics/MOCHA/actions/workflows/build.yaml/badge.svg?branch=ros2)](https://github.com/KumarRobotics/MOCHA/actions/workflows/build.yaml)
+
 ![MOCHA gif](mocha.gif)
 
 This repository contains the distributed and opportunistic communication stack used for multi-robot experiments at KumarRobotics.