add joind.in as alternative

README.md

@@ -10,6 +10,7 @@
 | [eventoL](http://eventol.github.io/eventoL/) | [GitHub](https://github.com/eventoL/eventoL) | mature | Python | GPLv3 |
 | [GetTogether](https://gettogether.community/) | [GitHub](https://github.com/GetTogetherComm/GetTogether) | mature | Python | BSD 2-Clause | 
 | [Gospeak](https://www.gospeak.fr/) | [GitHub](https://github.com/loicknuchel/gospeak) | mature | Scala | Apacke 2.0 |
+| [joind.in](https://joind.in/) | [GitHub](https://github.com/joindin/joindin-web2) | mature | PHP | BSD 3-Clause |
 | [Mobilizon](https://joinmobilizon.org/en/) | [framagit.org](https://framagit.org/framasoft/mobilizon/) | in development | Elixir | AGPL | 
 | [on_ruby](https://www.onruby.eu/) | [GitHub](https://github.com/phoet/on_ruby) | mature | Ruby | (extended) Beer-ware | 
 | Open Event | GitHub: [Frontend](https://github.com/fossasia/open-event-frontend), [Backend](https://github.com/fossasia/open-event-server) | mature | Python | Apache 2.0 & GPLv3 |