Fix documentation for `Step 0` to `Step 1` in `docker build`

The indexing of steps in the output of `docker build` starts with `Step 1`.
However, there are several places in the docs that start with `Step 0`.

This fix addresses the issue and changes `Step 0` to `Step 1` (and subsequent steps).

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

docs/reference/builder.md

@@ -86,15 +86,15 @@ the `Using cache` message in the console output.
 
     $ docker build -t svendowideit/ambassador .
     Sending build context to Docker daemon 15.36 kB
-    Step 0 : FROM alpine:3.2
+    Step 1 : FROM alpine:3.2
      ---> 31f630c65071
-    Step 1 : MAINTAINER SvenDowideit@home.org.au
+    Step 2 : MAINTAINER SvenDowideit@home.org.au
      ---> Using cache
      ---> 2a1c91448f5f
-    Step 2 : RUN apk update &&      apk add socat &&        rm -r /var/cache/
+    Step 3 : RUN apk update &&      apk add socat &&        rm -r /var/cache/
      ---> Using cache
      ---> 21ed6e7fbb73
-    Step 3 : CMD env | grep _TCP= | (sed 's/.*_PORT_\([0-9]*\)_TCP=tcp:\/\/\(.*\):\(.*\)/socat -t 100000000 TCP4-LISTEN:\1,fork,reuseaddr TCP4:\2:\3 \&/' && echo wait) | sh
+    Step 4 : CMD env | grep _TCP= | (sed 's/.*_PORT_\([0-9]*\)_TCP=tcp:\/\/\(.*\):\(.*\)/socat -t 100000000 TCP4-LISTEN:\1,fork,reuseaddr TCP4:\2:\3 \&/' && echo wait) | sh
      ---> Using cache
      ---> 7ea8aef582cc
     Successfully built 7ea8aef582cc

docs/reference/commandline/build.md

@@ -231,12 +231,12 @@ specify an arbitrary Git repository by using the `git://` or `git@` scheme.
 $ docker build -f ctx/Dockerfile http://server/ctx.tar.gz
 
 Downloading context: http://server/ctx.tar.gz [===================>]    240 B/240 B
-Step 0 : FROM busybox
+Step 1 : FROM busybox
  ---> 8c2e06607696
-Step 1 : ADD ctx/container.cfg /
+Step 2 : ADD ctx/container.cfg /
  ---> e7829950cee3
 Removing intermediate container b35224abf821
-Step 2 : CMD /bin/ls
+Step 3 : CMD /bin/ls
  ---> Running in fbc63d321d73
  ---> 3286931702ad
 Removing intermediate container fbc63d321d73