Add contributing instructions

CONTRIBUTING.md

@@ -0,0 +1,27 @@
# Contributing to YogCrypt

If you have questions or comments, please feel free to email the maintainers. 

For feature requests, suggestions, and bug reports, please open an issue on
[our Github](https://github.com/yogcrypt/yogcrypt).  (Or, send us
an email if you're opposed to using Github for whatever reason.)

Patches are welcomed as pull requests on
[our Github](https://github.com/yogcrypt/yogcrypt), as well as by
email (preferably sent to all of the maintainers listed in `README.md`).

All issues on YogCrypt are mentored, if you want help with a bug, feel free to
contact us.

Some issues are easier than others. The `easy` label and `good first issue` can
be used to find the easy issues. If you want to work on an issue, please leave a
comment so that we can assign it to you!

# Code of Conduct

We follow the [Rust Code of Conduct](http://www.rust-lang.org/conduct.html),
with the following additional clauses:

* We respect the rights to privacy and anonymity for contributors and people in
  the community.  If someone wishes to contribute under a pseudonym different to
  their primary identity, that wish is to be respected by all contributors.

README.md

@@ -1,4 +1,6 @@
# YogCrypt [![Build Status](https://travis-ci.com/yogcrypt/yogcrypt.svg?branch=master)](https://travis-ci.com/yogcrypt/yogcrypt)
# YogCrypt

[![Build Status](https://travis-ci.com/yogcrypt/yogcrypt.svg?branch=master)](https://travis-ci.com/yogcrypt/yogcrypt)

**A fast, general purpose crypto library in pure Rust.**

@@ -8,6 +10,11 @@ YogCrypt currently provides three cryptographic algorithms in Chinese National
Standard, namely the SM2 cryptographic asymmetric algorithm, the SM3
cryptographic hash algorithm, and the SM4 block cipher algorithm.

## Contributing

YogCrypt is maintained by @liuwenling, @Messjer, and @mssun. Please see
[CONTRIBUTING.md](CONTRIBUTING.md) for more information.

## License

YogCrypt is distributed under the terms of both the MIT license and the Apache