Contributions.md

[InDieTasten]

I am interested in using and also contributing to CSharp.lua

It would be very helpful to have a Contributions.md for you to state, whether you welcome contributions, and if you do, then how to get started and some direction as to what parts need the most work.

Also, it would be very useful to provide English documentation, as there is no chance (for me) to read the chinese documentation ;D

Thanks for your work

[yanghuan]

Thanks for your report, I will add them later.