Update readme

README.md

@@ -9,6 +9,7 @@
 </p>
 
 <p align="center">
+  <a href="#about">About</a> •
   <a href="#development">Development</a> •
   <a href="#documentation">Documentation</a> •
   <a href="#support-and-feedback">Support</a> •
@@ -17,33 +18,31 @@
   <a href="#licensing">Licensing</a>
 </p>
 
+## About
+
+This repository contains the source code of the Digital Green Certificates Wallet App for iOS.
+
+The wallet app provides a user interface to store and manage personal DGCs directly on the phone. DGCs will be imported by scanning a base45-encoded QR code and decoding CBOR to JSON. Afterwards, it is symmetrically encrypted in the app’s sandbox and the symmetric key is stored in the system’s keychain. Multiple DGCs can be stored in the app. Access to the app is controlled via biometric data (e. g., Touch ID or Face ID). The wallet app can display any imported DGC as QR code for scanning and verifying with the verifier app.
+
 ## Development
 
 ### Prerequisites
 
-- [ ] TODO
+- [ ] TODO: Describe prerequisites
 
 ### Build
 
 Whether you cloned or downloaded the 'zipped' sources you will either find the sources in the chosen checkout-directory or get a zip file with the source code, which you can expand to a folder of your choice.
 
 In either case open a terminal pointing to the directory you put the sources in. The local build process is described afterwards depending on the way you choose.
 
-#### XYZ (Maven, ...) based build
-
-- [ ] TODO
-
-#### Build Docker Image
-
-- [ ] TODO
-
-#### API documentation  
+#### XYZ (Maven, Docker ...) based build
 
-- [ ] TODO
+- [ ] TODO: Add instructions for different build types
 
 ## Documentation  
 
-- [ ] TODO
+- [ ] TODO: Link to documentation
 
 ## Support and feedback