Merge pull request nestjs#1983 from Tony133/docs/openapi-update

docs(openapi): update setup options for fastify

Author: kamilmysliwiec

content/openapi/introduction.md

@@ -137,10 +137,10 @@ const document = SwaggerModule.createDocument(app, config, options);
 
 #### Setup options
 
-You can configure Swagger UI by passing the options object which fulfills the `SwaggerCustomOptions` interface as a fourth argument of the `SwaggerModule#setup` method.
+You can configure Swagger UI by passing the options object which fulfills the `ExpressSwaggerCustomOptions` (if you use express) interface as a fourth argument of the `SwaggerModule#setup` method.
 
 ```TypeScript
-export interface SwaggerCustomOptions {
+export interface ExpressSwaggerCustomOptions {
   explorer?: boolean;
   swaggerOptions?: Record<string, any>;
   customCss?: string;
@@ -155,6 +155,14 @@ export interface SwaggerCustomOptions {
 }
 ```
 
+If you use fastify, you can configure the user interface by passing the `FastifySwaggerCustomOptions` object.
+
+```Typescript
+export interface FastifySwaggerCustomOptions {
+  uiConfig?: Record<string, any>;
+}
+```
+
 For example, if you want to make sure that the authentication token persists after refreshing the page, or change the page title (that shows up in the browser), you can use the following settings:
 
 ```TypeScript