Add README and LICENSE

Author: andrewbranch

LICENSE

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+Copyright 2019 Andrew Branch
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README.md

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+# react-use-hover
+
+A React state hook to determine whether a React element is being hovered.
+
+## Installation
+
+```
+npm install react-use-hover
+```
+
+## Usage
+
+```js
+import useHover from 'react-use-hover';
+
+function Tooltip() {
+  const [isHovering, hoverProps] = useHover();
+  return (
+    <>
+      <span {...hoverProps} aria-describedby="overlay">Hover me</span>
+      <Overlay visible={isHovering} role="tooltip" id="overlay">
+        I’m a lil popup or something!
+      </Overlay>
+    </>
+  );
+}
+```
+
+### Options
+
+```js
+useHover({
+  mouseEnterDelayMS,
+  mouseLeaveDelayMS
+})
+```
+
+- **`mouseEnterDelayMS: number = 200`**. The number of milliseconds to delay before setting the `isHovering` state to `true`. (Mousing back out during this delay period will cancel the state change.)
+- **`mouseLeaveDelayMS: number = 0`**. The number of milliseconds to delay before setting the `isHovering` state to `false`. (Mousing back in during this period will cancel the state change.)
+
+## Testing
+
+```bash
+# Run once, with coverage
+npm run test
+
+# Watch mode
+npm run test -- --watch
+
+# Do whatever you want
+npx jest # --any --jest --options
+```
+
+## Contributing
+
+PRs welcome! Please ensure you `npm run build` and commit before pushing (to run prettier) and maintain 100% test coverage.