You might have seen icons on Github repos like these: 🐛 ✅🔥 📦 👽 These are nothing but emojis that are common across internet and is also available on Github. Below are links which provide code for such emojis.
Official API that provides key and links of available emojis in JSON format, which are usuable in Github commits, pull-requests, etc.
This page contains exhaustive cheat sheets that are not only useful for Github but also on many code collabaration and social media websites and tools.