manifest.json

{
  "name": "NPM Link",
  "version": "1.1",
  "description": "Link NPM packages on GitHub with their npm registry page.",
  "manifest_version": 2,
  "permissions": ["*://*.github.com/*"],
  "content_scripts": [
    {
      "matches": ["*://*.github.com/*"],
      "js": ["script.js"],
      "run_at": "document_end"
    }
  ],
  "icons": {
    "48": "icon48.png"
  }
}