docs: add notice linking to analysis_server_plugin
Closes https://github.com/dart-lang/sdk/pull/61820
GitOrigin-RevId: f45bed09b1360eeb3ff1119caf3edc188fdc27af
Change-Id: I77d6708b9a52fe40ed81a9e99e12b7df4ab01f2f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/457580
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Samuel Rawlins <srawlins@google.com>
diff --git a/pkg/analyzer_plugin/README.md b/pkg/analyzer_plugin/README.md
index ef7af1b..bb5aa47 100644
--- a/pkg/analyzer_plugin/README.md
+++ b/pkg/analyzer_plugin/README.md
@@ -3,6 +3,13 @@
A framework for building plugins for the analysis server.
+> **WARNING!**
+> This package is for **legacy support** and is **not recommended** for new plugin development.
+>
+> For modern plugin implementations, use the [`analysis_server_plugin`](https://pub.dev/packages/analysis_server_plugin) package instead.
+>
+> See its documentation for the latest architecture and examples.
+
## Usage
**Note:** The plugin support is not currently available for general use.
