Update file README.md

README.md

@@ -24,8 +24,9 @@ For implementing this environment, we used the GNS3 tool. It is an open-source s
 
 ## Graph modeling 
 
+<center>
 <img src="image.png" alt="alt text" width="500" />
-
+</center>
 
 ## Key Features
 
@@ -50,7 +51,7 @@ This work is supported by the French National Research Agency (ANR) under grant
 ## License
 Creative Commons Attribution. CC BY 4.0 Deed Attribution 4.0 International.
 
-![Alt text](image-3.png)
+<img src="image-3.png" alt="alt text" width="250" />
 
 ## Project status
 Current