Expose docker's root directory by default as part of docker info.

Signed-off-by: Vishnu kannan <vishnuk@google.com>
Upstream-commit: 6a3176d4fee3e747ecb6b2d27ab2eb68471f3f8f
Component: engine

components/engine/docs/reference/commandline/info.md

@@ -44,6 +44,7 @@ For example:
     Total Memory: 62.86 GiB
     Name: docker
     ID: I54V:OLXT:HVMM:TPKO:JPHQ:CQCD:JNLC:O3BZ:4ZVJ:43XJ:PFHZ:6N2S
+    Docker Root Dir: /var/lib/docker
     Debug mode (client): true
     Debug mode (server): true
      File Descriptors: 59