Examine source code of Github Download Button

{
  "manifest_version": 2,
  "name": "Github Download Button",
  "version": "1.0.0",
  "description": "Adds a download button on Github files",
  "icons": {
    "19": "icon_19.png",
    "48": "icon_48.png",
    "96": "icon_96.png",
    "128": "icon_128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.github.com/*"
      ],
      "js": [
        "main.js"
      ]
    }
  ],
  "permissions": [
    "*://*.github.com/*",
    "*://raw.githubusercontent.com/*",
    "webRequest"
  ]
}