Adding Shhh to "Custom communication systems".

README.md

@@ -307,6 +307,7 @@ _CalDAV or CardDAV web-based clients._
 - [Tuber](https://blog.trailofbits.com/2015/12/15/self-hosted-video-chat-with-tuber/) - Peer-to-peer video chat that works. ([Source Code](https://github.com/trailofbits/tubertc)) `MIT` `Javascript`
 - [ZeroNet](https://zeronet.io/) `⚠` - Open, free, and uncensorable websites, using Bitcoin cryptography and BitTorrent network. ([Source Code](https://github.com/HelloZeroNet/ZeroNet)) `GPL-2.0` `Python`
 - [Zulip](https://zulip.org) - Zulip is a powerful, open source group chat application. ([Source Code](https://github.com/zulip/zulip)) `Apache-2.0/Other` `Python`
+- [Shhh](https://github.com/smallwat3r/shhh) - Keep secrets out of emails or chat logs, share them using secure links with passphrase and expiration dates. ([Source Code](https://github.com/smallwat3r/shhh)) `MIT` `Python`
 
 ### Email