Update Proxmox/ThunderboltNetwork.md

Proxmox/ThunderboltNetwork.md

@@ -11,6 +11,12 @@ apt install -y lldpd
 
 Mandatory packages.
 ```python
+apt install -y lsb-release
+curl -s https://deb.frrouting.org/frr/keys.gpg | sudo tee /usr/share/keyrings/frrouting.gpg > /dev/null
+FRRVER="frr-stable"
+echo deb '[signed-by=/usr/share/keyrings/frrouting.gpg]' https://deb.frrouting.org/frr \
+     $(lsb_release -s -c) $FRRVER | sudo tee -a /etc/apt/sources.list.d/frr.list
+apt update
 apt install -y frr
 ```