remove rainloop

- unmaintained since May 2021
- unaddressed security issues
- ref. https://github.com/awesome-selfhosted/awesome-selfhosted/pull/2814

README.md

@@ -438,7 +438,6 @@ Mailing lists servers and mass mailing software - one message to many recipients
 - [Isotope Mail](https://blog.marcnuri.com/isotope-mail-client-introduction/) - Microservice based webmail client built with ReactJS and Spring. ([Source Code](https://github.com/manusa/isotope-mail)) `Apache-2.0` `Docker/Java`
 - [MailCare](https://mailcare.io) - Open source disposable email address service. ([Source Code](https://github.com/mailcare/mailcare)) `MIT` `PHP`
 - [Mailpile](https://www.mailpile.is/) - Webmail client with search, filtering, encryption features and more. ([Source Code](https://github.com/mailpile/Mailpile)) `AGPL-3.0` `Python`
-- [RainLoop](https://www.rainloop.net/) - Simple, modern and fast webmail with IMAP/SMTP Support and multi accounting. ([Demo](https://mail.rainloop.net), [Source Code](https://github.com/RainLoop/rainloop-webmail)). `AGPL-3.0` `PHP`
 - [Roundcube](https://roundcube.net) - Browser-based IMAP client with an application-like user interface. ([Source Code](https://github.com/roundcube/roundcubemail)) `GPL-3.0` `PHP`
 - [SquirrelMail](https://squirrelmail.org) - Another browser-based IMAP client. ([Source Code](https://sourceforge.net/p/squirrelmail/code/HEAD/tree/)) `GPL-2.0` `PHP`