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> •
@@ -17,35 +18,31 @@
   <a href="#licensing">Licensing</a>
 </p>
 
-- [ ] TODO
+## About
+
+This repository contains the source code of the Digital Green Certificates App Core for Android.
+
+The app core provides shared functionality for the [verifier](https://github.com/eu-digital-green-certificates/dgca-verifier-app-android) and [wallet](https://github.com/eu-digital-green-certificates/dgca-wallet-app-android) apps.
 
 ## 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