Gerrit v3.14 release notes: instructions to enable the AI Chat

Add specific instructions on how to enable the AI Chat in
Gerrit v3.14, with a reference to a sample plugin developed by
GerritForge that integrates Gerrit with Google's Gemini AI.

Change-Id: I341637ee92eac8096e9e7dc111265b5a97b33dfe

pages/site/releases/3.14.md

diff --git a/pages/site/releases/3.14.md b/pages/site/releases/3.14.md
index 57d2e58..706d02b 100644
--- a/pages/site/releases/3.14.md
+++ b/pages/site/releases/3.14.md
@@ -38,6 +38,15 @@
 The AI model can also expose custom actions, which are going to be rendered
 by Gerrit in the "AI Chat" sidebar.
 
+To enable the "Review Agent" panel, install one plugin that implements the Gerrit's
+`AiCodeReviewProvider` (e.g. GerritForge's [ai-review-agent-gemini](https://github.com/GerritForge/ai-review-agent-gemini/))
+and enable the "AI Chat" experiment in `gerrit.config`:
+
+```ini
+[experiments]
+  enabled = UiFeature__enable_ai_chat
+```
+
 ### WebUI Modernization
 
 The WebUI has been improved by removing all the legacy Polymer dependencies