add docs for commit --change

Docker-DCO-1.1-Signed-off-by: Daniel, Dao Quang Minh <dqminh89@gmail.com> (github: dqminh)

Docker-DCO-1.1-Signed-off-by: Dan Walsh <dwalsh@redhat.com> (github: rhatdan)

docs/sources/reference/commandline/cli.md

@@ -694,6 +694,7 @@ you refer to it on the command line.
     Create a new image from a container's changes
 
       -a, --author=""     Author (e.g., "John Hannibal Smith <hannibal@a-team.com>")
+      -c, --change=[]     Apply a modification in Dockerfile format before committing the image
       -m, --message=""    Commit message
       -p, --pause=true    Pause container during commit
 
@@ -720,6 +721,19 @@ If this behavior is undesired, set the 'p' option to false.
     REPOSITORY                        TAG                 ID                  CREATED             VIRTUAL SIZE
     SvenDowideit/testimage            version3            f5283438590d        16 seconds ago      335.7 MB
 
+#### Commit an existing container with new configurations
+
+    $ sudo docker ps
+    ID                  IMAGE               COMMAND             CREATED             STATUS              PORTS
+    c3f279d17e0a        ubuntu:12.04        /bin/bash           7 days ago          Up 25 hours
+    197387f1b436        ubuntu:12.04        /bin/bash           7 days ago          Up 25 hours
+    $ sudo docker inspect -f "{{ .Config.Env }}" c3f279d17e0a
+    [HOME=/ PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin]
+    $ sudo docker commit --change "ENV DEBUG true" c3f279d17e0a  SvenDowideit/testimage:version3
+    f5283438590d
+    $ sudo docker inspect -f "{{ .Config.Env }}" f5283438590d
+    [HOME=/ PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin DEBUG=true]
+
 ## cp
 
 Copy files/folders from a container's filesystem to the host