Add --service-ports note to ports section (#12658)

* Add --service-ports note to ports section

## Description

Add note in `ports` section of file reference docs pointing to the `run` command's `--service-ports` flag

## Motivation

Spent quite a few hours spinning my wheels before I came across `run`'s `--service-ports` flag.

I'm struggling to find the issue where I found this, but the comment pointing to `--service-ports` had a lot of reacts, so this might be a relatively common 

## Things I'd still like to do

- [ ] link to the [`--service-ports` docs](https://github.com/docker/docker.github.io/blob/master/compose/reference/run.md) -- not sure how to do this
- [ ] clean up location of this note -- not sure if I've put the note in a good place -- we can shunt it to the bottom
- [ ] Duplicate for older versions

Thanks

* Minor style update

Co-authored-by: Usha Mandya <47779042+usha-mandya@users.noreply.github.com>

compose/compose-file/compose-file-v3.md

@@ -1641,6 +1641,10 @@ Expose ports.
 >
 > Port mapping is incompatible with `network_mode: host`
 
+> **Note**
+>
+> `docker-compose run` ignores `ports` unless you include `--service-ports`.
+
 #### Short syntax
 
 There are three options: