Update technical-overview.md doc with current code (#86)

com.apple.container.defaults default subnet key must be network.subnet,
not default.subnet.


https://github.com/apple/container/blob/ef4462ead7449eba48c0b682b93e30930047f9ef/Sources/Services/ContainerNetworkService/AllocationOnlyVmnetNetwork.swift#L70

Author: vadikgo

docs/technical-overview.md

@@ -85,7 +85,7 @@ Normally, vmnet creates the container network using the CIDR address 192.168.64.
   - Run `container system stop` to terminate the services for `container`.
   - Using the macOS `defaults` command, update the default subnet value used by the network helper process. For example, if the bridge address shown by `ifconfig` is 192.168.66.1, run:
     ```bash
-    defaults write com.apple.container.defaults default.subnet 192.168.66.1/24
+    defaults write com.apple.container.defaults network.subnet 192.168.66.1/24
     ```
   - Run `container system start` to launch services again.
   - Try running the container again and verify that its IP address matches the current bridge interface value.