contrib: cni: provide example CNI configurations

This also updates the readme to no longer contain CNI configuration
information (which had incorrect steps), and rather just points to the
example configs.

Signed-off-by: Aleksa Sarai <asarai@suse.de>

contrib/cni/10-ocid-bridge.conf

@@ -0,0 +1,15 @@
+{
+    "cniVersion": "0.2.0",
+    "name": "ocid-bridge",
+    "type": "bridge",
+    "bridge": "cni0",
+    "isGateway": true,
+    "ipMasq": true,
+    "ipam": {
+        "type": "host-local",
+        "subnet": "10.88.0.0/16",
+        "routes": [
+            { "dst": "0.0.0.0/0" }
+        ]
+    }
+}

contrib/cni/99-loopback.conf

@@ -0,0 +1,4 @@
+{
+    "cniVersion": "0.2.0",
+    "type": "loopback"
+}

contrib/cni/README.md

@@ -0,0 +1,16 @@
+## `contrib/cni` ##
+
+There are a wide variety of different [CNI][cni] network configurations. This
+directory just contains some example configurations that can be used as the
+basis for your own configurations (distibutions should package these files in
+example directories).
+
+To use these configurations, place them in `/etc/cni/net.d` (or the directory
+specified by `ocid.network.network_dir` in your `ocid.conf`).
+
+In addition, you need to install the [CNI plugins][cni] necessary into
+`/opt/cni/bin` (or the directory specified by `ocid.network.plugin_dir`). The
+two plugins necessary for the example CNI configurations are `loopback` and
+`bridge`.
+
+[cni]: https://github.com/containernetworking/cni