Add documentation

README.md

@@ -118,6 +118,38 @@ POSTGRES_DB = "hyperion"
 uvicorn app.main:app --reload
 ```
 
+## Use Alembic migrations
+
+The project use Alembic migrations to manage database structure evolutions.
+
+When the database does not exist, SQLAlchemy will create a new database with an up to date structure. When the database already exist, migrations must be run to update the structure.
+
+### Run migrations
+
+These [migration files](./migrations/versions/) are automatically run before Hyperion startup.
+
+They can also be run manually using the following command:
+
+```bash
+alembic upgrade head
+```
+
+> If you want to force Alembic to consider your database structure is up to date, you can use the following command:
+>
+> ```bash
+> alembic stamp head
+> ```
+
+### Write migration files
+
+To create a new migration file, use the following command:
+
+```bash
+alembic revision --autogenerate -m "Your message"
+```
+
+Files must be names with the following convention: `number-message.py
+
 ## OpenAPI specification
 
 API endpoints are parsed following the OpenAPI specifications at `http://127.0.0.1:8000/openapi.json`.