initial attempt to make better readme

No, Y2Logger is child of ::Logger, so you need to use something like
```
@log = Yast::Y2Logger.new
@log.info "do something"
```
and Yast::Logger is module that provide method log, so you can avoid instantiation. see https://github.com/yast/yast-ruby-bindings/blob/master/src/ruby/yast/y2logger.rb#L70