feat(graphql): add mercurius plugins to docs

Author: tugascript

content/graphql/plugins.md

@@ -1,6 +1,6 @@
 ### Plugins
 
-> warning **Warning** This chapter applies only to the `@nestjs/apollo` driver.
+#### For `@nestjs/apollo` driver
 
 Plugins enable you to extend Apollo Server's core functionality by performing custom operations in response to certain events. Currently, these events correspond to individual phases of the GraphQL request lifecycle, and to the startup of Apollo Server itself (read more [here](https://www.apollographql.com/docs/apollo-server/integrations/plugins/)). For example, a basic logging plugin might log the GraphQL query string associated with each request that's sent to Apollo Server.
 
@@ -51,3 +51,31 @@ GraphQLModule.forRoot({
 ```
 
 > info **Hint** The `ApolloServerOperationRegistry` plugin is exported from the `apollo-server-plugin-operation-registry` package.
+
+#### For `@nestjs/mercurius` driver
+
+Some mercurius specific fastify plugins have to be loaded after the mercurius plugin (read more [here](https://mercurius.dev/#/docs/plugins)) on the plugin tree.
+
+> warning **Warning** [mercurius-upload](https://github.com/mercurius-js/mercurius-upload) is an exception and should be registered in the main file.
+
+There is an optional `plugins` array parameter inside the `MercuriusDriver`, this array takes an object with the plugin function on the `plugin` parameter and its options inside an optional `options` parameter. Therefore, registering the [cache plugin](https://github.com/mercurius-js/cache) would be as follows:
+
+```typescript
+GraphQLModule.forRoot({
+  driver: MercuriusDriver,
+  // ...
+  plugins: [
+    {
+      plugin: cache,
+      options: {
+        ttl: 10,
+        policy: {
+          Query: {
+            add: true
+          }
+        }
+      },
+    }
+  ]
+}),
+```