Add floating IP instructions to OpenStack deploy docs

deploy/README.md

@@ -61,6 +61,20 @@ openstack server create \
   devbox-vm
 ```
 
+#### Floating IP
+
+OpenStack doesn't support assigning a floating IP at instance creation time — it's a separate step after the VM is active:
+
+```bash
+# Allocate a new floating IP from the external network
+openstack floating ip create <external-network>
+
+# Assign it to the VM
+openstack server add floating ip devbox-vm <floating-ip>
+```
+
+To find your external network name: `openstack network list --external`. If you already have an unassigned floating IP, skip the create step.
+
 The VM boots with Docker installed, firewall configured (or skipped on OpenStack), and your SSH key authorized. Log in as the `devbox` user.
 
 ### Console password (optional)