updated README.md

[whatwouldmarvindo]

added a section to the readme on how to dynamically update the sliderOptions. For this I simply added a short snippet of code like this

Dynamically update slider options

export class myComponent {
    @ViewChild('mySlider') slider: NouisliderComponent

    updateSliderOptions() {
        this.slider.slider.updateOptions(configObject)
    }
}

<nouislider #mySlider></nouislider>

This is my first PR, please be gentle :)