Add support for alternative routes definition

This patch allows configuring linux routing table by defining
global routers instead of per-interface routes. Per-interface
routes are then implicitly inferred from matching routers.

Change-Id: Ie09e63399c870778368a6dde7e37fe4b49a1dc88
Closes-Bug: PROD-26896
(cherry picked from commit c4730b1c895245ddae6ddf5f9f8619180d2569a0)
diff --git a/README.rst b/README.rst
index 9c66374..a8373d3 100644
--- a/README.rst
+++ b/README.rst
@@ -1484,6 +1484,57 @@
                 netmask: 255.255.255.0
                 gateway: 192.168.0.1
 
+Linux networks with implicit routes definition:
+
+- on node 1:
+
+.. code-block:: yaml
+
+    linux:
+      network:
+        enabled: true
+        router:
+          ctl:
+            # router that connects 10.0.1.0/24 and 10.0.2.0/24
+            addresses:
+              - 10.0.1.1/24
+              - 10.0.2.1/24
+          test:
+            addresses:
+              - 10.0.1.2/24
+            networks:
+              - 10.100.0.0/16
+        interface:
+          ctl:
+            name: eth0
+            address: 10.0.1.101
+            netmask: 255.255.255.0
+
+- on node2:
+
+.. code-block:: yaml
+
+    linux:
+      network:
+        enabled: true
+        router:
+          ctl:
+            # equivalent of node1's ctl router with 'implicit_routes = false'
+            options:
+              implicit_routes: false
+            addresses:
+              - 10.0.1.1/24
+              - 10.0.2.1/24
+            networks:
+              - 10.0.1.0/24
+              - 10.0.2.0/24
+        interface:
+          ctl:
+            name: eth0
+            address: 10.0.2.101
+            netmask: 255.255.255.0
+
+
 Native Linux Bridges:
 
 .. code-block:: yaml