Update README

Short description and (planned) features.

README.md

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-# harbour-nextcloudnotes
-Nextcloud notes client for SailfishOS
+# Nextcloud notes client for SailfishOS
+
+A mobile App providing access to [Nextcloud Notes](https://github.com/nextcloud/notes) on [Sailfish OS](https://sailfishos.org).  
+Communication with the nextcloud server happens over the [Notes API 0.2](https://github.com/nextcloud/notes/wiki/API-0.2).  
+The [Sailfish OS SDK](https://sailfishos.org/wiki/Application_SDK) is used to write and build this project.  
+
+## Current features
+
+- List all notes on the server
+- Show the content of the notes
+- Toggle favorite property
+- Group notes by category
+
+## Planned features
+
+(The ordering represents the priority for the implementation)
+- Login screen for the nextcloud account
+- Create new notes
+- Delete notes
+- Edit notes
+- Automatically push changes to the server while editing a note
+- [Markdown](https://en.wikipedia.org/wiki/Markdown) rendering
+- Search in notes
+- Checklist support
+- Offline support
+- Usage of [Sailfish OS Secrets](https://sailfishos.org/wiki/Secrets_and_Crypto) to store the user credentials
+
+## Features to be considered
+
+- All features of the [Android App](https://github.com/stefan-niedermann/nextcloud-notes)
+- Multiple nextcloud accounts
+- Share notes
+- Import notes from textfiles
+- Sync with the Sailfish OS build in notes app
+- Versioning / trashbin