docs: update project name (#74)

README.md

@@ -1,5 +1,5 @@
 <h1 align="center">
-    EU Digital Green Certificates Gateway
+   EU Digital COVID Certificate Gateway
 </h1>
 
 <p align="center">
@@ -32,7 +32,7 @@
 
 ## About
 
-This repository contains the source code of the Digital Green Certificates Gateway (DGCG).
+This repository contains the source code of the EU Digital COVID Certificate Gateway (DGCG).
 
 DGCG is used to share validation and verification information across all national backend servers. By using DGCG,
 backend-to-backend integration is facilitated, and countries can onboard incrementally, while the national backends