As is raised in 26312, in `docker network ls`, the help output was
mistaken to `volume names`:
```
-q, --quiet Only display volume names
```
This fix changes the help output to:
```
-q, --quiet Only display network IDs
```
This fix also updates the documentation in:
`docs/reference/commandline/network_ls.md`
This fix fixes 26312.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>