docs(cli): add info about how to install specific plugin version

closes #6434

docs/sources/plugins/installation.md

@@ -34,11 +34,16 @@ List available plugins
 grafana-cli plugins list-remote
 ```
 
-Install a plugin type
+Install the latest version of a plugin
 ```
 grafana-cli plugins install <plugin-id>
 ```
 
+Install a specific version of a plugin
+```
+grafana-cli plugins install <plugin-id> <version>
+```
+
 List installed plugins
 ```
 grafana-cli plugins ls