Update APi in the readme

[vincenzopalazzo]

I wrote the readme a lot of time ago, and I'm a very bad people to make this task.

I discovered that the API about the log level is old, we need to change it from

   @RPCMethod(
            name = "annotation_hello",
            description = "Annotation plugin"
    )
    public void hello(CLightningPlugin plugin, CLightningJsonObject request, CLightningJsonObject response) {
        log(CLightningLevelLog.WARNING, request.toString());
        response.add("type", "random");
    }

To

   @RPCMethod(
            name = "annotation_hello",
            description = "Annotation plugin"
    )
    public void hello(CLightningPlugin plugin, CLightningJsonObject request, CLightningJsonObject response) {
        log(PluginLog.WARNING, request.toString());
        response.add("type", "random");
    }

[mhechavarria]

Can I work on this, please?

[vincenzopalazzo]

@mhechavarria all yours

[mhechavarria]

Done, please review it: #59