docs: add GitHub discussion badge (#1547)

Author: snitin315

README.md

@@ -8,7 +8,7 @@
 [![node][node]][node-url]
 [![tests][tests]][tests-url]
 [![coverage][cover]][cover-url]
-[![chat][chat]][chat-url]
+[![discussion][discussion]][discussion-url]
 [![size][size]][size-url]
 
 # webpack-dev-middleware
@@ -578,8 +578,8 @@ Please take a moment to read our contributing guidelines if you haven't yet done
 [tests-url]: https://github.com/webpack/webpack-dev-middleware/actions
 [cover]: https://codecov.io/gh/webpack/webpack-dev-middleware/branch/master/graph/badge.svg
 [cover-url]: https://codecov.io/gh/webpack/webpack-dev-middleware
-[chat]: https://badges.gitter.im/webpack/webpack.svg
-[chat-url]: https://gitter.im/webpack/webpack
+[discussion]: https://img.shields.io/github/discussions/webpack/webpack
+[discussion-url]: https://github.com/webpack/webpack/discussions
 [size]: https://packagephobia.com/badge?p=webpack-dev-middleware
 [size-url]: https://packagephobia.com/result?p=webpack-dev-middleware
 [docs-url]: https://webpack.js.org/guides/development/#using-webpack-dev-middleware