docker_network resource doc in README is out-of-date

[mattlqx]

The README does not specify newer attributes for docker_network like internal and driver_opts. It would be helpful if the docs were up-to-date so it's easier to discover the functionality.

[JMLayn]

I got driver_opts to work by doing:

docker_network 'docker_gwbridge' do
  driver 'bridge'
  subnet '172.17.1.0/24'
  gateway '172.17.1.1'
  driver_opts 'com.docker.network.bridge.enable_icc' => 'false', 'com.docker.network.bridge.enable_ip_masquerade' => 'true', 'com.docker.network.bridge.name' => 'docker_gwbridge'