Merge pull request #14483 from jack-w-shaw/JUJU-1660_improve_scp_help…

…_text

#14483

- ~[ ] Code style: imports ordered, good names, simple structure, etc~
- ~[ ] Comments saying why design decisions were made~
- ~[ ] Go unit tests, with comments saying what you're testing~
- ~[ ] [Integration tests](https://github.com/juju/juju/tree/develop/tests), with comments saying what you're testing~
- ~[ ] [doc.go](https://discourse.charmhub.io/t/readme-in-packages/451) added or updated in changed packages~

## QA steps

```sh
$ juju help scp
...
 # Copy a file ('chunks-inspect') from localhost to /loki directory
 # in a specific container in a juju unit running in Kubernetes:
 juju scp --container loki chunks-inspect loki-k8s/0:/loki
...
```

cmd/juju/commands/scp.go

@@ -105,6 +105,10 @@ Examples:
     # (-- -3):
     juju scp -- -3 0:file.dat foo/0:
 
+    # Copy a file ('chunks-inspect') from localhost to /loki directory
+    # in a specific container in a juju unit running in Kubernetes:
+    juju scp --container loki chunks-inspect loki-k8s/0:/loki
+
 See also: 
 	ssh
 `