Update plugins.md on how to bundle a plugin. (#3004)

* Update plugins.md on how to bundle a plugin.

* Update src/guide/reusability/plugins.md

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Co-authored-by: Natalia Tepluhina <[email protected]>

Author: luckydonald

Diff for: src/guide/reusability/plugins.md

@@ -135,3 +135,7 @@ export default {
 ```
 
 </div>
+
+### Bundle for NPM
+
+If you further want to build and publish your plugin for others to use, see [Vite's section on Library Mode](https://vitejs.dev/guide/build.html#library-mode).