docs: fix link to command-line reference
This link worked on GitHub, but was broken on docs.docker.com, so
replacing with a regular link directly to the docs instead.
@@ -122,7 +122,7 @@ enabled, and use it to create a volume.
To disable a plugin, use the `docker plugin disable` command. To completely
remove it, use the `docker plugin remove` command. For other available
commands and options, see the
-[command line reference](../reference/commandline/index.md).
+[command line reference](https://docs.docker.com/engine/reference/commandline/cli/).
## Developing a plugin
