Update local-executors.md

Change path for generation of my-plugin to libs/my-plugin

nx g @nx/plugin:plugin libs/my-plugin

This makes it work with the plugin executor generate command.

docs/shared/recipes/plugins/local-executors.md

@@ -10,7 +10,7 @@ If you don't already have a local plugin, use Nx to generate one:
 
 ```shell {% skipRescope=true %}
 nx add @nx/plugin
-nx g @nx/plugin:plugin my-plugin
+nx g @nx/plugin:plugin libs/my-plugin
 ```
 
 Use the Nx CLI to generate the initial files needed for your executor.