external links: add links to more communities/forums (#3914)

-ref. https://old.reddit.com/r/selfhosted/comments/14cqjeb/the_subreddit_will_go_on_the_community_must_be/

README.md

@@ -2189,7 +2189,7 @@ _See also: [Wikimatrix](https://www.wikimatrix.org/), [Wiki Engines - WikiIndex]
 - Lists of software aimed at privacy and decentralization in some form: [PRISM Break](https://prism-break.org/en/), [privacytools.io](https://www.privacytools.io/), [Alternative Internet](https://redecentralize.github.io/alternative-internet/), [Libre Projects](https://libreprojects.net/)
 - [Easy Indie App](https://easyindie.app) - Apps that can be self-hosted in a few clicks.
 - Dynamic Domain Name services: [Afraid.org](https://freedns.afraid.org/domain/registry/), [Pagekite](https://pagekite.net/)
-- Communities/forums: [/r/selfhosted](https://www.reddit.com/r/selfhosted/), [IndieWeb](https://indieweb.org/)
+- Communities/forums: [/r/selfhosted on reddit](https://old.reddit.com/r/selfhosted/), [r-selfhosted forum](https://forum.r-selfhosted.com/), [/r/selfhosed Matrix Channel](https://matrix.to/#/#selfhosted:selfhosted.chat), [/c/selfhosted on lemmy.ml](https://lemmy.ml/c/selfhost), [/c/selfhosted on lemmy.world](https://lemmy.world/c/selfhosted), [/m/selfhosted on kbin.social](https://kbin.social/m/selfhosted), [Homelab forum](https://homelabforum.com/), [/r/homelab on reddit](https://old.reddit.com/r/homelab/), [IndieWeb](https://indieweb.org/)
 - Mirrors: [GitHub.com](https://github.com/awesome-selfhosted/awesome-selfhosted), [Gitlab.com](https://gitlab.com/awesome-selfhosted/awesome-selfhosted)
 - [theme.park](https://theme-park.dev/) - A collection of themes/skins for 50 selfhosted apps! ([Source Code](https://github.com/GilbN/theme.park/)) `MIT` `CSS`
 - [Track Awesome Selfhosted](https://www.trackawesomelist.com/awesome-selfhosted/awesome-selfhosted/) - Get the latest updates of awesome-selfhosted.