Add NVMe performance volume example to OpenStack deploy docs

deploy/README.md

@@ -36,9 +36,9 @@ openstack flavor list
 # Create the security group first (one-time, see below)
 ./setup-openstack-secgroup.sh
 
-# Create the VM
+# Basic — boot from default storage
 openstack server create \
-  --flavor m1.medium \
+  --flavor c4m8 \
   --image debian-13-trixie \
   --network my-network \
   --security-group opencode-devbox \
@@ -47,6 +47,20 @@ openstack server create \
   devbox-vm
 ```
 
+If your cloud offers NVMe-backed (performance) volumes, boot from one for faster Docker and build I/O:
+
+```bash
+# Performance — boot from NVMe volume (40GB, preserved on instance deletion)
+openstack server create \
+  --flavor c4m8 \
+  --network my-network \
+  --security-group opencode-devbox \
+  --key-name my-ssh-key \
+  --user-data cloud-init.yml \
+  --block-device source=image,id=$(openstack image show debian-13-trixie -f value -c id),dest=volume,size=40,shutdown=preserve,bootindex=0,volume_type=performance \
+  devbox-vm
+```
+
 The VM boots with Docker installed, firewall configured (or skipped on OpenStack), and your SSH key authorized. Log in as the `devbox` user.
 
 ### Option 2: Post-install script (manual)