add sharding-jdbc module readme

# Sharding-JDBC OpenTracing Plugin

## Introduction

The plugin will add [OpenTracing](http://opentracing.io/) instrumentation to Sharding-JDBC. This plugin makes it 

easy for developers using the Sharding-JDBC to incorporate the tracer that support OpenTracing.

## How to use

### Dependency

```xml

<dependency>

    <groupId>io.shardingjdbc</groupId>

    <artifactId>sharding-jdbc-opentracing</artifactId>

    <version>${latest.version}</version>

</dependency>

```

### Setting Tracer

There are two ways to incorporate `io.opentracing.Tracer` object(eg. [Zipkin](https://zipkin.io), [Skywalking](http://skywalking.org)) with this plugin.

#### 1. Using code to config plugin

 1. Get `io.opentracing.Tracer` object from Opentracing Tracer.

 1. Invoke `io.shardingjdbc.opentracing.ShardingJDBCTracer#init(io.opentracing.Tracer)` before using Sharding-JDBC components.

#### 2. Using jvm properties to config plugin

You can set a tracer implement to the plugin by following instrument.

 1. Set `-Dshardingjdbc.opentracing.tracer.class=OPENTRACING_TRACER_CLASS_NAME` to start the application. `OPENTRACING_TRACER_CLASS_NAME` MUST implement

`io.opentracing.Tracer

 1. Invoke `io.shardingjdbc.opentracing.ShardingJDBCTracer#init()` method before using Sharding-JDBC components.

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# Sharding-JDBC OpenTracing插件

## 介绍

该插件会将[OpenTracing](http://opentracing.io/)组件添加到Sharding-JDBC中。这个插件使

Sharding-JDBC的开发人员很容易整合支持OpenTracing的Tracer。

## 使用方法

### 添加依赖

```xml

<dependency>

    <groupId>io.shardingjdbc</groupId>

    <artifactId>sharding-jdbc-opentracing</artifactId>

    <version>${latest.version}</version>

</dependency>

```

### 设置Tracer

有两种方法可以整合插件与`io.opentracing.Tracer`对象（例如 [Zipkin](https://zipkin.io)，[Skywalking](http://skywalking.org)）。

#### 1. 使用代码

 1. 获得 `io.opentracing.Tracer`对象，该对象一般由Tracer提供.

 1. 使用Sharding-JDBC组件之前，调用 `io.shardingjdbc.opentracing.ShardingJDBCTracer#init(io.opentracing.Tracer)`.

#### 2. 使用jvm属性配置

 1. 设置 `-Dshardingjdbc.opentracing.tracer.class=OPENTRACING_TRACER_CLASS_NAME` 启动应用. `OPENTRACING_TRACER_CLASS_NAME` 必须实现

`io.opentracing.Tracer

 1. 使用Sharding-JDBC组件之前，调用 `io.shardingjdbc.opentracing.ShardingJDBCTracer#init()`.