add README.md in src/models

src/models/README.md

@@ -0,0 +1,46 @@
+# Custom models
+
+You may define custom models (entities) that will be registered on the global container by creating files in the `src/models` directory that export an instance of `BaseEntity`.
+
+## Example
+
+### 1. Create the Entity
+
+```ts
+// src/models/post.ts
+
+import { BeforeInsert, Column, Entity, PrimaryColumn } from "typeorm";
+import { BaseEntity} from "@medusajs/medusa";
+import { generateEntityId } from "@medusajs/medusa/dist/utils"
+
+@Entity()
+export class Post extends BaseEntity {
+  @Column({type: 'varchar'})
+  title: string | null;
+
+  @BeforeInsert()
+  private beforeInsert(): void {
+    this.id = generateEntityId(this.id, "post")
+  }
+}
+```
+
+### 2. Create the Migration
+
+You also need to create a Migration to create the new table in the database. See [How to Create Migrations](https://docs.medusajs.com/advanced/backend/migrations/) in the documentation.
+
+### 3. Create a Repository
+Entities data can be easily accessed and modified using [TypeORM Repositories](https://typeorm.io/working-with-repository). To create a repository, create a file in `src/repositories`. For example, here’s a repository `PostRepository` for the `Post` entity:
+
+```ts
+// src/repositories/post.ts
+
+import { EntityRepository, Repository } from "typeorm"
+
+import { Post } from "../models/post"
+
+@EntityRepository(Post)
+export class PostRepository extends Repository<Post> { }
+```
+
+See more about defining and accesing your custom [Entities](https://docs.medusajs.com/advanced/backend/entities/overview) in the documentation.