How to add an item to Quick Settings in Android

I was thinking if there is a way to add an item in Quick Settings Panel in android ? I have an app called Mirror by Koushik Dutta that does the same. It adds an item in Quick Settings panel. I decompiled the app and saw that he's moving the apk to /system/priv-app . That's it. Nothing's related to adding an item in Quick Settings Toggle. I know it'll require root access (just a college project). Please if anyone has any idea how it can be done, it would be really helpful.