This spike shows how to create and test locally an "Hello World" Google Chrome extension, serving as an introduction to extensions.
From my understanding, Chrome Extensions is a framework and your extension app is served/controlled using an manifest.json file, which describes how to load the extension. The schema of this file is described here: https://json.schemastore.org/chrome-manifest.json
Click on extensions button > Manage Extensions > Load unpacked > Navigate to extensions directory > Select
