feat(docs): add operation name

Author: vicary

internal/website/docs/client/fetching-data.mdx

@@ -60,6 +60,28 @@ if (possibleData instanceof Promise) {
 }
 ```
 
+### Operation name
+
+A custom operation name can be added to GraphQL queries, mutations and subscriptions.
+
+This is useful when mocking for unit tests, and advanced server logics.
+
+```ts
+import { query, resolved, inlineResolved } from '../gqty';
+
+resolved(() => query.helloWorld, { operationName: 'MyQuery' });
+
+inlineResolved(() => query.helloWorld, { operationName: 'MyQuery' });
+```
+
+Both `resolved` and `inlineResolved` above will generate the following query:
+
+```graphql
+query MyQuery {
+  helloWorld
+}
+```
+
 ## track
 
 The function `track` accepts a callback that gets automatically called every time related data arrives or related cache changes, particularly useful for subscriptions, but it also works for queries.