Merge pull request #16153 from calavera/missing_ps_placeholder

Add missing ps placeholder to the docs.

docs/reference/commandline/ps.md

@@ -173,6 +173,7 @@ Placeholder | Description
 `.Ports` | Exposed ports.
 `.Status` | Container status.
 `.Size` | Container disk size.
+`.Names` | Container names.
 `.Labels` | All labels assigned to the container.
 `.Label` | Value of a specific label for this container. For example `{{.Label "com.docker.swarm.cpu"}}`