docs(usage-guide): add alternative way to use classes

website/docs/usage-guide.mdx

@@ -175,22 +175,29 @@ export default {
 
 Specify functions for each method within the class. The main requirement is that it should be the default export.
 
-```js
-export default class Resource {
+```ts
+export default class SomeResource {
   get(req, res, routeParams) {
     const { documentId, draftId } = routeParams;
     res.end(`Requested document ${documentId} and his draft ${draftId}`);
   }
 
-  post(req, res, routeParams) {
-    const { documentId, draftId } = routeParams;
-    res.end(`Created draft ${draftId} for document ${documentId}`);
+  patch(req, res, routeParams) {
+    // ...
   }
+}
+```
 
-  patch(req, res, routeParams) {
+Alternatively, you can export a class instance:
+
+```ts
+class SomeResource {
+  get(req, res, routeParams) {
     // ...
   }
 }
+
+export default new SomeResource();
 ```
 
 ### Methods in Filenames