docs(vx-tooltip): add relative wrapper note in readme

packages/vx-tooltip/Readme.md

@@ -4,16 +4,19 @@
 npm install --save @vx/tooltip
 ```
 
-The `@vx/tooltip` package provides utilities for making it easy to add `Tooltip`s to a visualization and includes hooks, higher-order component (HOC) enhancers and Tooltip components.
+The `@vx/tooltip` package provides utilities for making it easy to add `Tooltip`s to a visualization
+and includes hooks, higher-order component (HOC) enhancers and Tooltip components.
 
 ### Hooks and Enhancers
 
 This package provides two ways to add tooltip state logic to your chart components:
 
-- a hook: `useTooltip()` 
+- a hook: `useTooltip()`
 - a higher order component (HOC): `withTooltip()`
 
-The `useTooltip` hook is the recommended way to add tooltip state logic to your components, but can only be used in functional components. The `withTooltip` HOC can be used with both functional and class components, and is the recommended way to add tooltip state logic to class components.
+The `useTooltip` hook is the recommended way to add tooltip state logic to your components, but can
+only be used in functional components. The `withTooltip` HOC can be used with both functional and
+class components, and is the recommended way to add tooltip state logic to class components.
 
 Both `useTooltip` and `withTooltip` expose the same values and functions for use in your component:
 
@@ -27,24 +30,37 @@ Both `useTooltip` and `withTooltip` expose the same values and functions for use
 | tooltipData   | any    | The `tooltipData` value passed to the `showTooltip` func, intended to be used for any data that your tooltip might need to render                     |
 | updateTooltip | func   | Call this function with the signature `func({ tooltipOpen, tooltipLeft, tooltipTop, tooltipData })` to set the tooltip state to the specified values. |
 
-In the case of `useTooltip`, these will be returned from the `useTooltip()` call in your component. In the case of `withTooltip`, they will be passed as props to your wrapped component. Refer to the [Examples](#examples) section for a basic demo of each approach.
+In the case of `useTooltip`, these will be returned from the `useTooltip()` call in your component.
+In the case of `withTooltip`, they will be passed as props to your wrapped component. Refer to the
+[Examples](#examples) section for a basic demo of each approach.
 
 #### useTooltip()
 
-If you would like to add tooltip state logic to a functional component, you may use the `useTooltip()` hook which will return an object with several properties that you can use to manage the tooltip state of your component.
+If you would like to add tooltip state logic to a functional component, you may use the
+`useTooltip()` hook which will return an object with several properties that you can use to manage
+the tooltip state of your component. **For correct tooltip positioning, it is important to wrap your
+component in an element (e.g., `div`) with `relative` positioning**. This is handled for you by the
+`withTooltip` HOC, but not with the `useTooltip()` hook.
 
 #### withTooltip(BaseComponent [, containerProps [, renderContainer]])
 
-If you would like to add tooltip state logic to a class component, you may wrap it in `withTooltip(BaseComponent [, containerProps [, renderContainer])`.
+If you would like to add tooltip state logic to a class component, you may wrap it in
+`withTooltip(BaseComponent [, containerProps [, renderContainer])`.
 
-The HOC will wrap your component in a `div` with `relative` positioning by default and handle state for tooltip positioning, visibility, and content by injecting the following props into your `BaseComponent`:
+The HOC will wrap your component in a `div` with `relative` positioning by default and handle state
+for tooltip positioning, visibility, and content by injecting the following props into your
+`BaseComponent`:
 
-You may override the container by specifying `containerProps` as the second argument to `withTooltip`, or by specifying `renderContainer` as the third argument to `withTooltip`.
+You may override the container by specifying `containerProps` as the second argument to
+`withTooltip`, or by specifying `renderContainer` as the third argument to `withTooltip`.
 
 ### Components
+
 #### Tooltip
 
-This is a simple Tooltip container component meant to be used to actually render a Tooltip. It accepts the following props, and will spread any additional props on the tooltip container div (i.e., ...restProps):
+This is a simple Tooltip container component meant to be used to actually render a Tooltip. It
+accepts the following props, and will spread any additional props on the tooltip container div
+(i.e., ...restProps):
 
 | Name      | Type             | Default | Description                                                                   |
 | :-------- | :--------------- | :------ | :---------------------------------------------------------------------------- |
@@ -57,7 +73,10 @@ This is a simple Tooltip container component meant to be used to actually render
 
 #### TooltipWithBounds
 
-This tooltip component is exactly the same as `Tooltip` above, but it is aware of its boundaries meaning that it will flip left/right and bottom/top based on whether it would overflow its parent's boundaries. It accepts the following props, and will spread any additional props on the Tooltip component (i.e., ...restProps):
+This tooltip component is exactly the same as `Tooltip` above, but it is aware of its boundaries
+meaning that it will flip left/right and bottom/top based on whether it would overflow its parent's
+boundaries. It accepts the following props, and will spread any additional props on the Tooltip
+component (i.e., ...restProps):
 
 | Name        | Type   | Default | Description                                                                                                                                                                      |
 | :---------- | :----- | :------ | :------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
@@ -68,9 +87,11 @@ This tooltip component is exactly the same as `Tooltip` above, but it is aware o
 | style       | object | --      | Sets / overrides any styles on the tooltip container (including top and left)                                                                                                    |
 | children    | node   | --      | Sets the children of the tooltip, i.e., the actual content                                                                                                                       |
 
-Note that this component is positioned using a `transform`, so overriding `left` and `top` via styles may have no effect.
+Note that this component is positioned using a `transform`, so overriding `left` and `top` via
+styles may have no effect.
 
 ### Examples
+
 #### useTooltip For Functional Components
 
 ```js