Splitting out the cli command into parts.

Signed-off-by: Mary Anthony <mary@docker.com>

docs/reference/commandline/diff.md

@@ -0,0 +1,39 @@
+<!--[metadata]>
++++
+title = "diff"
+description = "The diff command description and usage"
+keywords = ["list, changed, files, container"]
+[menu.main]
+parent = "smn_cli"
+weight=1
++++
+<![end-metadata]-->
+
+# diff
+
+    Usage: docker diff CONTAINER
+
+    Inspect changes on a container's filesystem
+
+List the changed files and directories in a container᾿s filesystem
+ There are 3 events that are listed in the `diff`:
+
+1. `A` - Add
+2. `D` - Delete
+3. `C` - Change
+
+For example:
+
+    $ docker diff 7bb0e258aefe
+
+    C /dev
+    A /dev/kmsg
+    C /etc
+    A /etc/mtab
+    A /go
+    A /go/src
+    A /go/src/github.com
+    A /go/src/github.com/docker
+    A /go/src/github.com/docker/docker
+    A /go/src/github.com/docker/docker/.git
+    ....