Update download buttons in readme (sindresorhus#263)

Author: fregante

readme.md

@@ -1,17 +1,17 @@
 # <img src="source/icon.png" width="45" align="left"> Notifier for GitHub
 
-[link-cws]: https://chrome.google.com/webstore/detail/notifier-for-github/lmjdlojahmbbcodnpecnjnmlddbkjhnn "Version published on Chrome Web Store"
-[link-amo]: https://addons.mozilla.org/en-US/firefox/addon/notifier-for-github/ "Version published on Mozilla Add-ons"
-
 > Browser extension - Get notified about new GitHub notifications
 
 Checks for new GitHub notifications every minute, shows the number of notifications you have, and shows desktop notifications as well.
 
 ## Install
 
-- [**Chrome** extension][link-cws] [<img valign="middle" src="https://img.shields.io/chrome-web-store/v/lmjdlojahmbbcodnpecnjnmlddbkjhnn.svg?label=%20">][link-cws]
-- [**Firefox** add-on][link-amo] [<img valign="middle" src="https://img.shields.io/amo/v/notifier-for-github.svg?label=%20">][link-amo]
-- **Opera** extension: Use [this Opera extension](https://addons.opera.com/en/extensions/details/download-chrome-extension-9/) to install the Chrome version.
+[link-chrome]: https://chrome.google.com/webstore/detail/notifier-for-github/lmjdlojahmbbcodnpecnjnmlddbkjhnn 'Version published on Chrome Web Store'
+[link-firefox]: https://addons.mozilla.org/en-US/firefox/addon/notifier-for-github/ 'Version published on Mozilla Add-ons'
+
+[<img src="https://raw.githubusercontent.com/alrra/browser-logos/90fdf03c/src/chrome/chrome.svg" width="48" alt="Chrome" valign="middle">][link-chrome] [<img valign="middle" src="https://img.shields.io/chrome-web-store/v/lmjdlojahmbbcodnpecnjnmlddbkjhnn.svg?label=%20">][link-chrome] also compatible with [<img src="https://raw.githubusercontent.com/alrra/browser-logos/90fdf03c/src/edge/edge.svg" width="24" alt="Edge" valign="middle">][link-chrome] [<img src="https://raw.githubusercontent.com/alrra/browser-logos/90fdf03c/src/opera/opera.svg" width="24" alt="Opera" valign="middle">][link-chrome]
+
+[<img src="https://raw.githubusercontent.com/alrra/browser-logos/90fdf03c/src/firefox/firefox.svg" width="48" alt="Firefox" valign="middle">][link-firefox] [<img valign="middle" src="https://img.shields.io/amo/v/notifier-for-github.svg?label=%20">][link-firefox]
 
 ## Highlights