Add social.dickseven.com

New instance

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

@@ -14,5 +14,6 @@ List of Known Mastodon instances
 | [gnusocial.me](https://gnusocial.me) |Yes, it's a mastodon instance now|Yes|
 | [icosahedron.website](https://icosahedron.website/) |Icosahedron-themed (well, visually), open registration.|Yes|
 | [memetastic.space](https://memetastic.space) |Memes|Yes|
+| [social.diskseven.com](https://social.diskseven.com) |Single user|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).