Added Bird 1.6 vs 2.0 changes

docs/bird_config.md

@@ -0,0 +1,44 @@
+Configuring Bird
+================
+
+## Bird 1.6 and 2.0 differences
+
+Bird 1.6's bird6 (which is what we will use) doesn't prefix anything
+with `ipv6` as they are assumed to all be IPv6. However, in bird 2.0,
+it is dual-stack and hence one must provide either an `ipv6` prefix or
+`ipv4` (we will of course be using the former).
+
+### Changes
+
+#### Table definitions
+
+So for example in 1.6 bird6 a table definition is as follows:
+
+```bird
+table crxn;
+```
+
+However in bird 2.0 it is as follows:
+
+```bird
+ipv6 table crxn;
+```
+
+#### Channels
+
+So for example in 1.6 bird6 a channel definition is as follows:
+
+```bird
+import all;
+export all;
+```
+
+However in bird 2.0 it is as follows:
+
+```bird
+ipv6 {
+	export all;
+	import all;	
+};
+```
+