/info: Add keys Architecture, OSType

- introduces Swarm-relevant keys, see #13634
  - docs updated

Signed-off-by: Olle Jonsson <olle.jonsson@gmail.com>

docs/reference/commandline/info.md

@@ -31,6 +31,8 @@ For example:
     Execution Driver: native-0.2
     Logging Driver: json-file
     Kernel Version: 3.19.0-22-generic
+    OSType: linux
+    Architecture: amd64
     Operating System: Ubuntu 15.04
     CPUs: 24
     Total Memory: 62.86 GiB

man/docker-info.1.md

@@ -44,6 +44,8 @@ Here is a sample output:
      Network: bridge null host
     Kernel Version: 3.13.0-24-generic
     Operating System: Ubuntu 14.04 LTS
+    OSType: linux
+    Architecture: amd64
     CPUs: 1
     Total Memory: 2 GiB