docs: ticket booking system guide (#13471)

* docs: ticket booking system guide

* fix vale error

www/apps/resources/app/how-to-tutorials/tutorials/preorder/page.mdx

@@ -279,7 +279,7 @@ Find all methods generated by the `MedusaService` in [the Service Factory refere
 
 </Note>
 
-### Export Module Definition
+### d. Export Module Definition
 
 The final piece to a module is its definition, which you export in an `index.ts` file at its root directory. This definition tells Medusa the name of the module and its service.
 
@@ -303,7 +303,7 @@ You use the `Module` function to create the module's definition. It accepts two
 
 You also export the module's name as `PREORDER_MODULE` so you can reference it later.
 
-### Add Module to Medusa's Configurations
+### e. Add Module to Medusa's Configurations
 
 Once you finish building the module, add it to Medusa's configurations to start using it.
 
@@ -322,7 +322,7 @@ module.exports = defineConfig({
 
 Each object in the `modules` array has a `resolve` property, whose value is either a path to the module's directory, or an `npm` package’s name.
 
-### Generate Migrations
+### f. Generate Migrations
 
 Since data models represent tables in the database, you define how they're created in the database with migrations. A migration is a TypeScript class that defines database changes made by a module.