message: updated README for slider example
diff: ## Slider
  -A bar and a handle that selects a single value from a range of values.
  -Can be oriented both vertical and horizontal.
  +A `Slider` is a bar and a handle that selects a single value from a range of values.
  +There exists both `Slider` and `VerticalSlider` depending on which orientation you need.
  <div align="center">
  <img src="sliders.gif">
  