Add Turtl as Keep alternative

README.md

@@ -158,6 +158,7 @@ These Firefox extensions can help prevent connections to Google domains and also
 - Keep
   - [Joplin](https://joplinapp.org/) - Open-source notes/todo app. Available for Windows, macOS, Linux, Android, and iOS. Also offers a terminal version. It can import Evernote `.enex` files if you use that. It can also sync with Nextcloud (mentioned above).
   - [Standard Notes](https://standardnotes.org/) - Encrypted note storage with loads of features. Offers a web app as well as downloads for most operating systems. Has a paid plan, but the free tier has many useful features as well.
+  - [Turtl](https://turtlapp.com/) - Encrypted collaborative notebook with possibility of running your own server.
   - [Zoho Notebook](https://www.zoho.com/notebook/) - A notebook from Zoho. Also available on Android.
   - [QOwnNotes](https://www.qownnotes.org/) - Open-source file editor with Markdown support. (thanks u/maqp2)
 - Play Music & Play Movies and TV