docs(private-networks): add RFC 6598 address range

Author: carmstrong

docs/_includes/_private-network.rst

@@ -1,3 +1,3 @@
 Due to changes introduced in Docker 1.3.1 related to insecure Docker registries, the hosts running
-Deis must be able to communicate via a private network in one of the RFC1918 private address spaces:
-``10.0.0.0/8``, ``172.16.0.0/12``, or ``192.168.0.0/16``.
+Deis must be able to communicate via a private network in one of the RFC 1918 or RFC 6598 private
+address spaces: ``10.0.0.0/8``, ``172.16.0.0/12``, ``192.168.0.0/16``, or ``100.64.0.0/10``.