docs: add missing details related to links and migrations (#11809)

* docs: add missing details related to links and migrations

* reorder content

* small changes

* last changes

* improve examples

* fix lint error

www/apps/book/app/learn/fundamentals/data-models/write-migration/page.mdx

@@ -23,17 +23,17 @@ Alternatively, you can manually create a migration file under the `migrations` d
 
 For example:
 
-```ts title="src/modules/hello/migrations/Migration20240429.ts"
+```ts title="src/modules/blog/migrations/Migration20240429.ts"
 import { Migration } from "@mikro-orm/migrations"
 
 export class Migration20240702105919 extends Migration {
 
   async up(): Promise<void> {
-    this.addSql("create table if not exists \"my_custom\" (\"id\" text not null, \"name\" text not null, \"created_at\" timestamptz not null default now(), \"updated_at\" timestamptz not null default now(), \"deleted_at\" timestamptz null, constraint \"my_custom_pkey\" primary key (\"id\"));")
+    this.addSql("create table if not exists \"author\" (\"id\" text not null, \"name\" text not null, \"created_at\" timestamptz not null default now(), \"updated_at\" timestamptz not null default now(), \"deleted_at\" timestamptz null, constraint \"author_pkey\" primary key (\"id\"));")
   }
 
   async down(): Promise<void> {
-    this.addSql("drop table if exists \"my_custom\" cascade;")
+    this.addSql("drop table if exists \"author\" cascade;")
   }
 
 }
@@ -43,7 +43,7 @@ The migration's file name should be of the format `Migration{YEAR}{MONTH}{DAY}.t
 
 In the `up` and `down` method of the migration class, you use the `addSql` method provided by MikroORM's `Migration` class to run PostgreSQL syntax.
 
-In the example above, the `up` method creates the table `my_custom`, and the `down` method drops the table if the migration is reverted.
+In the example above, the `up` method creates the table `author`, and the `down` method drops the table if the migration is reverted.
 
 <Note title="Tip">
 
@@ -76,10 +76,18 @@ This reflects the changes in the database as implemented in the migration's `up`
 To rollback or revert the last migration you ran for a module, run the following command:
 
 ```bash
-npx medusa db:rollback helloModuleService
+npx medusa db:rollback blog
 ```
 
-This rolls back the last ran migration on the Hello Module.
+This rolls back the last ran migration on the Blog Module.
+
+### Caution: Rollback Migration before Deleting
+
+If you need to delete a migration file, make sure to rollback the migration first. Otherwise, you might encounter issues when generating and running new migrations.
+
+For example, if you delete the migration of the Blog Module, then try to create a new one, Medusa will create a brand new migration that re-creates the tables or indices. If those are still in the database, you might encounter errors.
+
+So, always rollback the migration before deleting it.
 
 ---