Docs: mention subbreddit and Discord community in contributing guidelines

Author: julien-deramond

.github/CONTRIBUTING.md

@@ -18,7 +18,7 @@ the preferred channel for [bug reports](#bug-reports), [features requests](#feat
 and [submitting pull requests](#pull-requests), but please respect the following
 restrictions:
 
-- Please **do not** use the issue tracker for personal support requests. Stack Overflow ([`bootstrap-6`](https://stackoverflow.com/questions/tagged/bootstrap-6) tag), [our GitHub Discussions](https://github.com/twbs/bootstrap/discussions) or [IRC](/README.md#community) are better places to get help.
+- Please **do not** use the issue tracker for personal support requests. Stack Overflow ([`bootstrap-6`](https://stackoverflow.com/questions/tagged/bootstrap-6) tag), Reddit ([`r/bootstrap` subreddit](https://www.reddit.com/r/bootstrap/)), [our GitHub Discussions](https://github.com/twbs/bootstrap/discussions), [the community Discord](https://discord.gg/bZUvakRU3M), or [IRC](/README.md#community) are better places to get help.
 
 - Please **do not** derail or troll issues. Keep the discussion on topic and
   respect the opinions of others.