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/start.md

@@ -13,8 +13,9 @@ weight=1
 
     Usage: docker start [OPTIONS] CONTAINER [CONTAINER...]
 
-    Start one or more stopped containers
+    Start one or more containers
 
       -a, --attach=false         Attach STDOUT/STDERR and forward signals
+      --help=false               Print usage
       -i, --interactive=false    Attach container's STDIN