Added Bookmarking -> "Briefkasten" (#3038)

* Update README - Added Bookmarking - "Briefkasten"

* Update README.md

* Update README.md

README.md

@@ -235,6 +235,7 @@ _Related: [Polls and Events](#polls-and-events)_
 
 **[`^        back to top        ^`](#)**
 
+- [Briefkasten](https://github.com/ndom91/briefkasten) - Modern app for saving and managing your own bookmarks. Includes a browser extension. ([Demo](https://briefkasten.vercel.app)) `MIT` `Nodejs`
 - [dyu bookmarks](https://github.com/dyu/bookmarks) - Single-threaded/process bookmark app powered by leveldb and uWebSockets. Supports importing from Delicious and Chrome. ([Demo](https://dyuproject.com/bookmarks/)) `Apache-2.0` `Java`
 - [Espial](https://github.com/jonschoning/espial) - An open-source, web-based bookmarking server. `AGPL-3.0` `Haskell`
 - [Firefox Account Server](https://mozilla-services.readthedocs.io/en/latest/howtos/run-fxa.html) - This allows you to host your own Firefox accounts server. ([Source Code](https://github.com/mozilla/fxa)) `MPL-2.0` `Nodejs, Java`