message: Add demo and CodeSandbox example links to main package README
diff: @@ -24,11 +24,11 @@ Complete documentation is available at [react-querybuilder.js.org](https://react
  To use the official compatibility components as seen in the demo (select options from the Style dropdown), take a look at the packages under the [`@react-querybuilder` org on npmjs.com](https://www.npmjs.com/org/react-querybuilder). We currently support:
  -- [Ant Design](https://ant.design/) ([@react-querybuilder/antd](https://www.npmjs.com/package/@react-querybuilder/antd))
  -- [Bootstrap](https://getbootstrap.com/) ([@react-querybuilder/bootstrap](https://www.npmjs.com/package/@react-querybuilder/bootstrap))
  -- [Bulma](https://bulma.io/) ([@react-querybuilder/bulma](https://www.npmjs.com/package/@react-querybuilder/bulma))
  -- [Chakra UI](https://chakra-ui.com/) ([@react-querybuilder/chakra](https://www.npmjs.com/package/@react-querybuilder/chakra))
  -- [MUI](https://mui.com/) ([@react-querybuilder/material](https://www.npmjs.com/package/@react-querybuilder/material))
  +- [Ant Design](https://ant.design/) ([@react-querybuilder/antd](https://www.npmjs.com/package/@react-querybuilder/antd) - [demo](https://react-querybuilder.js.org/react-querybuilder/#style=antd), [usage](https://codesandbox.io/s/github/react-querybuilder/react-querybuilder/tree/main/examples/antd))
  +- [Bootstrap](https://getbootstrap.com/) ([@react-querybuilder/bootstrap](https://www.npmjs.com/package/@react-querybuilder/bootstrap) - [demo](https://react-querybuilder.js.org/react-querybuilder/#style=bootstrap), [usage](https://codesandbox.io/s/github/react-querybuilder/react-querybuilder/tree/main/examples/bootstrap))
  +- [Bulma](https://bulma.io/) ([@react-querybuilder/bulma](https://www.npmjs.com/package/@react-querybuilder/bulma) - [demo](https://react-querybuilder.js.org/react-querybuilder/#style=bulma), [usage](https://codesandbox.io/s/github/react-querybuilder/react-querybuilder/tree/main/examples/bulma))
  +- [Chakra UI](https://chakra-ui.com/) ([@react-querybuilder/chakra](https://www.npmjs.com/package/@react-querybuilder/chakra) - [demo](https://react-querybuilder.js.org/react-querybuilder/#style=chakra), [usage](https://codesandbox.io/s/github/react-querybuilder/react-querybuilder/tree/main/examples/chakra))
  +- [MUI](https://mui.com/) ([@react-querybuilder/material](https://www.npmjs.com/package/@react-querybuilder/material) - [demo](https://react-querybuilder.js.org/react-querybuilder/#style=material), [usage](https://codesandbox.io/s/github/react-querybuilder/react-querybuilder/tree/main/examples/material))
  ## Basic usage
  