add xenon documents.

Signed-off-by: LiJiansheng <[email protected]>

README.md

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+[![Build Status](https://travis-ci.org/radondb/xenon.png)](https://travis-ci.org/radondb/xenon)
+[![Go Report Card](https://goreportcard.com/badge/github.com/radondb/xenon)](https://goreportcard.com/report/github.com/radondb/xenon)
+[![codecov.io](https://codecov.io/gh/radondb/xenon/graphs/badge.svg)](https://codecov.io/gh/radondb/xenon/branch/master)
+
+# Xenon
+
+![](docs/images/xenon.png)
+
+## Overview
+
+`Xenon` is a MySQL HA and replication management tool using Raft protocol.
+
+* Fast Failover with no lost transactions
+* Streaming & Speed-Unmatched backup/restore
+* Mysql Operation and Maintenance
+* No central control and easy-to-deploy
+* As a Cloud App
+
+## Documentation
+
+- [build_and_run](docs/how_to_build_and_run_xenon.md) : How to build and run Xenon.
+- [client_commands](docs/xenoncli_commands.md) : Xenon client commands.
+- [how_xenon_works](docs/how_xenon_works.md) : How Xenon works.
+
+## Status
+
+Xenon is production ready, it has been used in production like [MySQL Plus](https://www.qingcloud.com/products/mysql-plus/)
+
+## Issues
+
+The [integrated github issue tracker](https://github.com/radondb/xenon/issues)
+is used for this project.
+
+## License
+
+Xenon is released under the GPLv3. See [LICENSE](LICENSE)