Add contribution guide

CONTRIBUTING.md

+Welcome! Any kinds of contributions are very welcomed. Please go through our contribution
+guide before you try to create a Pull Request for `jcli`.
+
+## CLI
+
+`jcli` is a command line interface. So a CLI framework is super important for us. Thanks to 
+[cobra](https://github.com/spf13/cobra). It powers us to do a better job.
+
+## Jenkins API
+
+API is another important part of this project. `jcli` manages your Jenkins by the HTTP API.
+There's no official documents for this. You can figure it by yourself, or just join our
+[gitter room](https://gitter.im/jenkinsci/jenkins-cli).
+
+## Testing
+
+We use a BDD Testing Framework to test our project. Please make sure you're familar
+with [ginkgo](https://github.com/onsi/ginkgo) before you get start to contribute.
+
+## Pull Requests
+
+Before you get start, please fork this project into your GitHub account firstly. Then
+create a git branch base on what you want to improve. Please consider **never** using
+the master branch as your develope branch. And the behaviour of the git **force push** is not
+encourage.
+
+Please **don't** create another Pull Request if you messed up your git commit records.
+
+In order to generate a nice [release notes](https://github.com/jenkins-zh/jenkins-cli/releases),
+please consider writing a proper Pull Request title.
+[release-draft](https://github.com/toolmantim/release-drafter) will generate the notes base your title.
+
+## Qulity
+
+Qulity is the heart of a project. So please make sure your Pull Request could pass the
+[Sonar Qulity Gate](https://sonarcloud.io/dashboard?id=jenkins-zh_jenkins-cli).
+
+|Metric|Operator|Value|
+|---|---|---|
+|Coverage|is less than|90.0%|
+|Duplicated Lines(%)|is greater than|3.0%|
+|Maintainablity Rating|is worse than|A|
+|Blocker Issues|is greater than|1|
+|Code Smells|is greater than|1|
+|Reliablity Rating|is worse than|A|
+|Security Rating|is worse than|A|
+
+## Good Start
+
+The [newbie](https://github.com/jenkins-zh/jenkins-cli/issues?q=is%3Aissue+is%3Aopen+label%3Anewbie) issues
+are the good start.

README-zh.md

@@ -55,4 +55,4 @@ sudo mv jcli /usr/local/bin/
 
 # 贡献
 
-该工具还处在非常早期的开发阶段，我们欢迎任何形式的贡献。
+如果你对该项目感兴趣，请首先仔细阅读我们的[贡献指南](CONTRIBUTING.md)。我们欢迎任何形式的贡献。

README.md

@@ -56,4 +56,5 @@ Read [this document](doc/README.md) to know more details about how to use `jcli`
 
 # Contribution
 
-It's still under very early develope time. Any contribution is welcome.
+If you're interested in this project. Please go through the
+[contribution guide](CONTRIBUTING.md). Any contributions are welcome.