docs: added to workflow legend + example improvements (#11895)

www/apps/book/app/learn/fundamentals/modules/service-constraints/page.mdx

@@ -13,17 +13,17 @@ Medusa wraps service method executions to inject useful context or transactions.
 For example, if you have a synchronous `getMessage` method, and you use it in other resources like workflows, Medusa executes it as an async method:
 
 ```ts
-await helloModuleService.getMessage()
+await blogModuleService.getMessage()
 ```
 
 So, make sure your service's methods are always async to avoid unexpected errors or behavior.
 
 ```ts highlights={[["8", "", "Method must be async."], ["13", "async", "Correct way of defining the method."]]}
 import { MedusaService } from "@medusajs/framework/utils"
-import MyCustom from "./models/my-custom"
+import Post from "./models/post"
 
-class HelloModuleService extends MedusaService({
-  MyCustom,
+class BlogModuleService extends MedusaService({
+  Post,
 }){
   // Don't
   getMessage(): string {
@@ -36,5 +36,5 @@ class HelloModuleService extends MedusaService({
   }
 }
 
-export default HelloModuleService
+export default BlogModuleService
 ```