Has a start-up doc to contribute the code?

[letsgo0]

I wanna add a tiny function，that is，barrier shares keyboard after one specified key pressed，not working otherwise.
So I think, it's necessary to know that， how barrier intercept keyboard and share it to another pc.
And I'am a newbie for c/c++. I found no doc resources to help me.
I would be very glad if anyone has a tip to me.