message: docs(slide docs): add slide plugin docs
diff: # observe-dom
  +Enable the ability to watch for changes of scroll dom. With this plugin, the refresh function will be called when the scroll elements change. It has the following features:
  +- debounce feature for css attributions which change frequently
  +- If the document element change occurs during the scroll animation, refresh will not be triggered.
  +
  +# Usage
  +
  +```js
  +import BScroll from 'BScroll'
  +import ObserveDom from 'ObserveDom'
  +BScroll.use(ObserveDom)
  +
  +new BScroll('.bs-wrap', {
  + //...
  + observeDom: true // set observeDom to true
  +})
  +```
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