Add theme.park to External links (#3641)

README.md

@@ -2179,6 +2179,7 @@ _See also: [Wikimatrix](https://www.wikimatrix.org/), [Wiki Engines - WikiIndex]
 - 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/)
 - 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.
 
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