Adding social.mashek.net

docs/Using-Mastodon/List-of-Mastodon-instances.md

@@ -16,5 +16,6 @@ List of Known Mastodon instances
 | [social.gestaltzerfall.net](https://social.gestaltzerfall.net) |Single user|No|No|
 | [mastodon.xyz](https://mastodon.xyz) |N/A|Yes|Yes|
 | [social.targaryen.house](https://social.targaryen.house) |N/A|Yes|No|
+| [social.mashek.net](https://social.mashek.net) |Themed and customised for Mashekstein Labs community. Selectively federates.|Yes|No|
 
 Let me know if you start running one so I can add it to the list! (Alternatively, add it yourself as a pull request).