[8.3] [docs] improve external plugin documentation (elastic#159431) (e…

…lastic#159473)

# Backport

This will backport the following commits from `main` to `8.3`:
- [[docs] improve external plugin documentation
(elastic#159431)](elastic#159431)

<!--- Backport version: 8.9.7 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

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BACKPORT-->

Co-authored-by: Thomas Watson <watson@elastic.co>

docs/developer/plugin/plugin-tooling.asciidoc

@@ -31,7 +31,7 @@ WARNING: {kib} distributable is not shipped with `@kbn/optimizer` anymore. You n
 
 You can leverage {kib-repo}blob/{branch}/packages/kbn-plugin-helpers[@kbn/plugin-helpers] to build a distributable archive for your plugin.
 The package transpiles the plugin code, adds polyfills, and links necessary js modules in the runtime.
-You don't need to install the `plugin-helpers`: the `package.json` is already pre-configured if you created your plugin with `node scripts/generate_plugin` script.
+You don't need to install the `plugin-helpers` dependency. If you created the plugin using `node scripts/generate_plugin` script, `package.json` is already pre-configured.
 To build your plugin run within your plugin folder:
 ["source","shell"]
 -----------