Add Dependabot badge to README (#40)

README.md

@@ -3,6 +3,7 @@
 [![Build Status](https://ci.jenkins.io/buildStatus/icon?job=Plugins/text-finder-plugin/master)](https://ci.jenkins.io/job/Plugins/job/text-finder-plugin/job/master/)
 [![Jenkins Plugin](https://img.shields.io/jenkins/plugin/v/text-finder.svg)](https://plugins.jenkins.io/text-finder)
 [![Jenkins Plugin Installs](https://img.shields.io/jenkins/plugin/i/text-finder.svg)](https://plugins.jenkins.io/text-finder)
+[![Dependabot Status](https://api.dependabot.com/badges/status?host=github&repo=jenkinsci/text-finder-plugin)](https://dependabot.com)
 
 This plugin lets you search for some text using regular expressions in a set of
 files or the console log. Once a match is found, you can downgrade a successful