add 'heimerdinger.lol' to external apps list

Author: rico-vz

README.md

@@ -85,6 +85,8 @@ Join the [Riot Games Third Party Developer Community](https://discordapp.com/inv
 
 * [Elo.rip](https://elo.rip/) - A chaotic champion randomizer.
 
+* [Heimerdinger.lol](https://heimerdinger.lol/) - Website dedicated to providing you with information about League of Legends. Such as Sale Rotations, Emotes and more.
+
 * [Skin Explorer](https://www.skinexplorer.lol) - Browse through League of Legends splash art from your browser.
 
 ## Content Creation