Added Reproducible Builds Section

Align the readme with the DP3T one

README.md

@@ -1,6 +1,9 @@
 # HA-AuthCode-Generation-Service (CovidCode-Service)
 HA-AuthCode-Generation-Service is an authorization code generation service for the CovidCode-UI and the proximity tracing app.
 
+# Reproducible Builds
+In order to have reproducible builds the io.github.zlika maven plugin is used. It replaces all timestamp with the timestamp of the last commit, and orders the entries in the JAR alphabetically. The github action then computes the sha256sum of the resulting JAR and adds the output as an build artifact.
+
 # Developer Instructions
 
 ## Initial setup