Docs: Add mill bundler under Third-party plugins (#2155)

Pull request: #2155

docs/antora/modules/ROOT/pages/Thirdparty_Plugins.adoc

@@ -1,4 +1,4 @@
-= Thirdparty Plugins
+= Third-Party Plugins
 :page-aliases: Thirdparty_Modules.adoc
 
 The Plugins in this section are developed/maintained outside the mill git tree.
@@ -71,6 +71,14 @@ Limited bash completion support.
 
 Project home: https://github.com/lefou/mill-bash-completion
 
+== Bundler
+
+`mill-bundler` is comparable to `scalajs-bundler` for SBT: It manages NPM dependencies for a Scala.js module and
+bundling it. Currently Webpack and Rollup are implemented but it's easy to use another one.
+
+Project home: https://github.com/nafg/mill-bundler
+
+
 == CI Release
 
 `mill-ci-release` is a wrapper around the existing publish functionality of