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>
Upstream-commit: 14e8898648909379f37049828e103ba1c97f253b
Component: engine

components/engine/docs/reference/commandline/exec.md

@@ -16,6 +16,7 @@ weight=1
     Run a command in a running container
 
       -d, --detach=false         Detached mode: run command in the background
+      --help=false               Print usage
       -i, --interactive=false    Keep STDIN open even if not attached
       --privileged=false         Give extended Linux capabilities to the command
       -t, --tty=false            Allocate a pseudo-TTY