Add profile photo

Author: kchristin22

_data/contributors.yml

@@ -317,7 +317,7 @@
   active: 1
 
 - name: "Christina Koutsou"
-  photo: 
+  photo: christina_koutsou.jpg
   info: "Google Summer of Code 2024 Contributor"
   email: [email protected]
   education: "Integrated Master's in Electrical and Computer Engineering, Aristotle University of Thessaloniki, Greece"