Add README.md content

Author: gilesgas

README.md

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 # simple-node-js-react-npm-app
+
+This repository is for the [Using Jenkins to build a Node.js/React project]( https://jenkins.io/doc/tutorials/using-jenkins-to-build-a-node-js-react-project/)
+tutorial in the [Jenkins User Documentation](https://jenkins.io/doc/).
+
+The repository contains a simple Node.js and React application which generates
+a web page with the content "Welcome to React" and is accompanied by a test to
+check that the application renders satisfactorily.
+
+The `jenkins` directory contains an example of the `Jenkinsfile` (i.e. Pipeline)
+you'll be creating yourself during the tutorial and the `scripts` directory
+contains a shell script with commands that are executed when Jenkins processes
+the "Deliver" stage of your Pipeline.