maven-os-plugin: Improve readme

[fzakaria]

        <extensions>
            <extension>
                <groupId>kr.motd.maven</groupId>
                <artifactId>os-maven-plugin</artifactId>
                <version>1.5.0.Final</version>
            </extension>
        </extensions>

Will give you the os name you can then use like

<classifier>${os.detected.name}</classifier>

[davidmoten]

Thanks!

[fzakaria]

Oh old comment :)