Add build badge

Author: PhilWakelin

README.md

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 cics-java-liberty-restapp
 ===========================
 
+[![Build](https://github.com/cicsdev/cics-java-liberty-restapp/actions/workflows/main.yml/badge.svg)](https://github.com/cicsdev/cics-java-liberty-restapp/actions/workflows/main.yml)
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 Sample RESTful web application for deployment to a Liberty JVM server in CICS. The application is supplied with two resources:
 
 1. `InfoResource` - This queries the JVM server environment using system properties and uses JAXB beans to return a JSON response detailing the CICS environment.