Fix man and commandline docs

- missing help option in `docs/reference/commandline/*.md` (some files
  have it, the other I fixed didn't)
- missing `[OPTIONS]` in Usage description
- missing options
- formatting
- start/stop idempotence

Signed-off-by: Antonio Murdaca <amurdaca@redhat.com>

docs/reference/commandline/diff.md

@@ -11,10 +11,12 @@ weight=1
 
 # diff
 
-    Usage: docker diff CONTAINER
+    Usage: docker diff [OPTIONS] CONTAINER
 
     Inspect changes on a container's filesystem
 
+      --help=false        Print usage
+
 List the changed files and directories in a container᾿s filesystem
  There are 3 events that are listed in the `diff`: