docs: fixups for plugin drivers in docker info

Plugin drivers were added to docker info in
https://github.com/docker/docker/pull/17300

but not added to the example output in the online
docs.

Also fixed mixed tabs/spaces in the API documentation.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

docs/reference/commandline/info.md

@@ -30,6 +30,9 @@ For example:
      Dirperm1 Supported: true
     Execution Driver: native-0.2
     Logging Driver: json-file
+    Plugins:
+     Volume: local
+     Network: bridge null host
     Kernel Version: 3.19.0-22-generic
     OSType: linux
     Architecture: x86_64