doc: add discord badge and deprecate gitter

README.md

@@ -3,7 +3,7 @@
 [![Chrome Web Store](https://img.shields.io/chrome-web-store/v/jinjaccalgkegednnccohejagnlnfdag.svg)](https://chrome.google.com/webstore/detail/violentmonkey/jinjaccalgkegednnccohejagnlnfdag)
 [![Firefox Add-ons](https://img.shields.io/amo/v/violentmonkey.svg)](https://addons.mozilla.org/firefox/addon/violentmonkey)
 [![Microsoft Edge Add-on](https://img.shields.io/badge/dynamic/json?label=microsoft%20edge%20add-on&query=%24.version&url=https%3A%2F%2Fmicrosoftedge.microsoft.com%2Faddons%2Fgetproductdetailsbycrxid%2Feeagobfjdenkkddmbclomhiblgggliao)](https://microsoftedge.microsoft.com/addons/detail/eeagobfjdenkkddmbclomhiblgggliao)
-[![Gitter](https://img.shields.io/gitter/room/violentmonkey/violentmonkey.svg)](https://gitter.im/violentmonkey/violentmonkey)
+[![Discord](https://img.shields.io/discord/995346102003965952?label=discord)](https://discord.gg/XHtUNSm6Xc)
 [![Subreddit subscribers](https://img.shields.io/reddit/subreddit-subscribers/ViolentMonkey)](https://www.reddit.com/r/ViolentMonkey/)
 
 Violentmonkey provides userscripts support for browsers.