message: docs(base-scroll-api): add docs for scrollTo
diff: @@ -77,7 +77,7 @@ BetterScroll provides a lot of flexible APIs, which are used when we implement s
  - `{number} y`, vertical axis distance. (unit: px)
  - `{number} time`, animation duration. (unit: ms)
  - `{Object} easing function`, usually don't suggest modifying. If you really need to modify, please refer `packages/shared-utils/src/ease.ts`'s of source code
  - - You only need to pass in this parameter if you want to modify some other properties of the CSS transform. The structure is as follows:
  + - `{Object} extraTransform`, you only need to pass in this parameter if you want to modify some other properties of the CSS transform. The structure is as follows:
  ```js
  let extraTransform = {
  // start point
  @@ -89,7 +89,10 @@ BetterScroll provides a lot of flexible APIs, which are used when we implement s
  scale: 1.1
  }
  }
  + bs.scrollTo(0, -60, 300, undefined, extraTransform)
  ```
  + - **Return**: none.
  + - **Usage**: scroll to specified position.
  ### scrollBy(x, y, time, easing)
  - **Arguments**:
  @@ -98,7 +101,7 @@ BetterScroll provides a lot of flexible APIs, which are used when we implement s
  - `{number} time`, animation duration. (unit: ms)
  - `{Object} easing function`, usually don't suggest modifying. If you really need to modify, please refer `packages/shared-utils/src/ease.ts`.
  - **Return**: none.
  - - **Usage**: Refer to current position, scroll the distance of (x, y).
  + - **Usage**: scroll to specified position based on current position.
  ### scrollToElement(el, time, offsetX, offsetY, easing)
  - **Arguments**:
  @@ -136,7 +139,7 @@ BetterScroll provides a lot of flexible APIs, which are used when we implement s
  - `{Function} fn`, callback
  - `{Object} context`,default is `this`.
  - **Return**: none
  - - **Usage**: Listen for a hook on the current BScroll, such as "scroll", "scrollEnd" and so on.
  + - **Usage**: listen for a hook on the current BScroll, such as "scroll", "scrollEnd" and so on.
  - **Example**:
  ```javascript
  import BScroll from '@BetterScroll/core'
  @@ -155,14 +158,14 @@ BetterScroll provides a lot of flexible APIs, which are used when we implement s
  - `{Function} fn`, callback
  - `{Object} context`, default is `this`.
  - **Return**: none
  - - **Usage**: Listen for a custom event, but only once. The listener will be removed once it triggers for the first time.
  + - **Usage**: listen for a custom event, but only once. The listener will be removed once it triggers for the first time.
  ### off(type, fn)
  - **Arguments**:
  - `{string} type`, event
  - `{Function} fn`, callback
  - **Return**: none
  - - **Usage**: Remove custom event listener. Only remove the listener for that specific callback.
  + - **Usage**: remove custom event listener. Only remove the listener for that specific callback.
  - **Example**:
  ```javascript
  import BScroll from '@BetterScroll/core'
  