Update README.md

Update Group number

Author: Nephelite

README.md

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 [![Review Assignment Due Date](https://classroom.github.com/assets/deadline-readme-button-22041afd0340ce965d47ae6ef1cefeee28c7c493a6346c4f15d667ab976d596c.svg)](https://classroom.github.com/a/bzPrOe11)
 # CS3219 Project (PeerPrep) - AY2425S1
-## Group: Gxx
+## Group: G25
 
 ### Note: 
 - You can choose to develop individual microservices within separate folders within this repository **OR** use individual repositories (all public) for each microservice.