Add readme of plugin.

docs/architecture/plugin.md

@@ -1 +1,41 @@
-# Plug-in
+# Plug-in
+
+**BotSharp** adopts a `plug-in` architecture design, and the modules are independent of each other. With `Conversation` as the core, each plug-in completes various functionalities (such as adding LLM provider and Text Embedding provider) through the Hook mechanism. Regarding the Hooks provided by the system, you can refer to the special [Hook section](hooks.md).
+
+Here we will introduce how to add a new plug-in to extend your LLM application. We still use the example of PizzaBot to illustrate how to complete this task.
+
+1. Add Class Library
+   Added a new class library called BotSharp.Plugin.PizzaBot and add referece to the web start application
+
+2. Implement Interface
+   Add a new class named `PizzaBotPlugin` and implement interface `IBotSharpPlugin`.
+    ```csharp
+    namespace BotSharp.Plugin.PizzaBot;
+
+    public class PizzaBotPlugin : IBotSharpPlugin
+    {
+        public void RegisterDI(IServiceCollection services, IConfiguration config)
+        {
+            // Register callback function
+            services.AddScoped<IFunctionCallback, MakePaymentFn>();
+
+            // Register hooks
+            services.AddScoped<IAgentHook, PizzaBotAgentHook>();
+        }
+    }    
+    ```
+
+3. Add to Settings
+   Add plugin to appsettings.json.
+    ```json
+    "PluginLoader": {
+        "Assemblies": [
+            "BotSharp.Plugin.PizzaBot"
+        ]
+    }
+    ```
+
+After starting the web project, you should see a successful loading message printed in the Console.
+```shell
+Loaded plugin PizzaBotPlugin from BotSharp.Plugin.PizzaBot.
+```