please include a contributing.md in your repo

[jinwei14]

It will be really helpful for people that want to contribute if you could include the contribution guide. It will be really helpful if you could include these topic:

1. language wish to implement
2. code format
3. file format

[jinwei14]

I intend to merge all my nice python code solution to your repo because I find your repo very helpful and I wants to contribute in to it.

请问contributor 是否可以让我整理的比较好的python 代码contribute 到你的库里？

我看还有很多pull request 没close 所以好奇是否可行？