Update docs of `docker network ls --filter`
Update docs of `docker network ls --filter`

Currently the help output of `docker network ls --filter` is:
```
Options:
  -f, --filter value   Provide filter values (i.e. 'dangling=true') (default [])
  ...
```
This caused confusion as only the following filters are supported at the moment:
 - `driver`
 - `type`
 - `name`
 - `id`
 - `label`

This fix update the help output of `docker network ls --filter` and `network_ls.md`.
The `dangling=true` description has been replace to:
```
Options:
  -f, --filter filter   Provide filter values (i.e. 'driver=bridge')
  ...
```

This fix fixes 28786.

Signed-off-by: Yong Tang <765086fe2e0c1f980161f127fec596800f327f62@outlook.com>

cpuguy83/cli,docker/cli,ashfall/cli,dnephin/cli,gdevillele/cli,allencloud/cli,redpanda/cli,thaJeztah/cli,e11137/cli,docker/cli,redpanda/cli,e11137/cli,Zebrilee/cli,riyazdf/cli,cpuguy83/cli,dnephin/cli,allencloud/cli,thaJeztah/cli,ashfall/cli,riyazdf/cli,Zebrilee/cli