Merge pull request #6052 from rhatdan/help

--help option and help command should print to stdout not stderr

docs/sources/reference/commandline/cli.md

@@ -15,6 +15,19 @@ or execute `docker help`:
 
       ...
 
+## Help
+To list the help on any command just execute the command, followed by the `--help` option.
+
+    $ sudo docker run --help
+
+    Usage: docker run [OPTIONS] IMAGE [COMMAND] [ARG...]
+
+    Run a command in a new container
+
+      -a, --attach=[]            Attach to STDIN, STDOUT or STDERR.
+      -c, --cpu-shares=0         CPU shares (relative weight)
+    ...
+
 ## Option types
 
 Single character commandline options can be combined, so rather than