edit pub eval readme

PUBLIC_EVALUATION_GUIDELINE.md

@@ -31,7 +31,9 @@ Once launched, you will receive an instance ID like `i-xxxxxx`.
 #### Step 1: Prepare Your SSH Key
 
 * When launching the instance, choose "Create new key pair" and download the `.pem` file (e.g. `osworld-host-key.pem`). Save it locally.
-<img src="./assets/pubeval1.png" alt="pubeval1" style="width:80%;" />
+<p align="center">
+  <img src="./assets/pubeval1.png" alt="pubeval1" style="width:80%;" />
+</p>
 
 * Set appropriate permissions:
 
@@ -43,15 +45,18 @@ Once launched, you will receive an instance ID like `i-xxxxxx`.
 
   - Go to the EC2 **Instances** page on the AWS Console.
   - Locate your Host instance by its ID.
-
+<p align="center">
   <img src="./assets/pubeval2.png" alt="pubeval2" style="width:80%;" />
+</p>
 
   * On the instance detail page:
 
     - **Public IP/DNS**: used for browser/VNC access and SSH connection
     - **Instance metadata**: e.g. storage, can be adjusted post-launch
 
+  <p align="center">
     <img src="./assets/pubeval3.png" alt="pubeval3" style="width:80%;" />
+  </p>
 
 #### Step 2: Connect via SSH or VSCode
 
@@ -74,12 +79,15 @@ Once launched, you will receive an instance ID like `i-xxxxxx`.
 
 Click on **Security Credentials** from the drop-down menu under your account in the top-right corner.
 
-<img src="./assets/pubeval4.png" alt="pubeval4" style="width: 25%;" />
+<p align="center">
+  <img src="./assets/pubeval4.png" alt="pubeval4" style="width: 25%;" />
+</p>
 
 In the **Access keys** section, click **"Create access key"** to generate your own key.
 
-<img src="./assets/pubeval5.png" alt="pubeval5" style="width: 80%;" />
-
+<p align="center">
+  <img src="./assets/pubeval5.png" alt="pubeval5" style="width: 80%;" />
+</p>
 
 ## 2. Environment Setup