chore: improve quickstart instructions

QUICKSTART.md

@@ -45,7 +45,15 @@ If you don’t already have an SSH key:
 bin/railiance gen-ssh-key
 ```
 
-Upload the public key to your cloud provider or VM host.
+### Upload your SSH public key to your cloud provider or VM host
+
+Once your key pair is generated (`~/.ssh/id_ed25519.pub`), copy the public key to the VM.  
+Replace `<IP>` with your server’s public IP and `<USER>` with the default login user (commonly `ubuntu` or `root`).
+
+```bash
+scp ~/.ssh/id_ed25519.pub <USER>@<IP>:/home/<USER>/authorized_keys.tmp
+ssh <USER>@<IP> "mkdir -p ~/.ssh && cat ~/authorized_keys.tmp >> ~/.ssh/authorized_keys && rm ~/authorized_keys.tmp && chmod 700 ~/.ssh && chmod 600 ~/.ssh/authorized_keys"
+```
 
 ---