readme: add coordinates to maven artifacts

[hastebrot]

The README.md could have a reference to the Maven artifacts. The shields badge automatically refers to the current version. I've also added snippets of other common ways to refer to the artifacts, which require to manually update the version string on every release.

As shields badge:

[![Maven](https://img.shields.io/maven-central/v/com.netopyr.reduxfx/reduxfx.svg?label=com.netopyr.reduxfx)](https://search.maven.org/#search|ga|1|com.netopyr.reduxfx)

As maven coordinates table:

| Group ID            | Artifact ID | Version |
| :-----------------: | :---------: | :-----: |
| com.netopyr.reduxfx | reduxfx     | 0.1.0   |

Group ID	Artifact ID	Version
com.netopyr.reduxfx	reduxfx	0.1.0

For maven pom xml:

<dependencies>
    <dependency>
        <groupId>com.netopyr.reduxfx</groupId>
        <artifactId>reduxfx</artifactId>
        <version>0.1.0</version>
    </dependency>
</dependencies>

For gradle build file:

dependencies {
    compile "com.netopyr.reduxfx:reduxfx:0.1.0"
}

As maven repository index url:

• http://central.maven.org/maven2/com/netopyr/reduxfx/reduxfx/
• https://mvnrepository.com/artifact/com.netopyr.reduxfx/reduxfx
• https://search.maven.org/#search|ga|1|com.netopyr.reduxfx

[netopyr]

Thanks a lot! You are absolutely right, this information belongs into the README.md