Add support for Mandarin

[aman-lj]

Hello,

I want to help add support for Mandarin so I created a course by exploring the internet and finding all the basic words, it doesn't have images etc yet but I plan to add that in future.

here is the repo: https://github.com/aman-lj/LibreLingo-ZH-fron-EN

feel free to contribute to it or give any suggestions. 😄