Added flatnotes to Note-taking & Editors (#3820)

Co-authored-by: nodiscc <nodiscc@gmail.com>

README.md

@@ -1430,6 +1430,7 @@ _Related: [Wikis](#wikis)_
 - [Dnote](https://www.getdnote.com) - A simple command line notebook with multi-device sync and web interface. ([Source Code](https://github.com/dnote/dnote)) `AGPL-3.0` `Go`
 - [DocPHT](https://docpht.org/) - With DocPHT you can take notes and quickly document anything and without the use of any database. ([Demo](https://demo.docpht.org/), [Source Code](https://github.com/docpht/docpht)) `MIT` `PHP`
 - [draw.io](https://draw.io) - Diagram software for making flowcharts, process diagrams, org charts, UML, ER and network diagrams. ([Source Code](https://github.com/jgraph/drawio)) `Apache-2.0` `Javascript`
+- [flatnotes](https://github.com/dullage/flatnotes) - A self-hosted, database-less note-taking web app that utilises a flat folder of markdown files for storage. ([Demo](https://demo.flatnotes.io)) `MIT` `Docker`
 - [HedgeDoc](https://demo.hedgedoc.org/) - Realtime collaborative markdown notes on all platforms, formerly known as CodiMD and HackMD CE. ([Source Code](https://github.com/hedgedoc/hedgedoc)) `AGPL-3.0` `Docker/Nodejs`
 - [Joplin](https://joplinapp.org/) - Joplin is a note taking application with Markdown editor and encryption support for mobile and desktop platforms. Runs client-side and syncs through self hosted Nextcloud or similar. Consider it like open source alternative to Evernote. ([Source Code](https://github.com/laurent22/joplin)) `MIT` `Nodejs`
 - [kiwix-serve](https://www.kiwix.org/en/downloads/kiwix-serve/) - HTTP daemon for serving wikis from ZIM files. ([Source Code](https://github.com/kiwix/kiwix-tools)) `GPL-3.0` `C++`