docs(migration): add details for migration process

migration/README.md

@@ -13,7 +13,9 @@ of the system.
 
 ## Current migration status
 
-The optional migration is available for DIVA **3.1.0**. You can use the migration service to upgrade from DIVA **>=3.0.0** and **<3.1.0**.
+The migration is available for DIVA **3.1.0**. Migration is **necessary** when the DSC is actively used in the production environment.
+It is also recommended to perform the migration so that the resources, added in the previous versions, can be deleted completely.
+You can use the migration service to upgrade from DIVA **>=3.0.0** and **<3.1.0**.
 
 Affected Components:
 
@@ -27,11 +29,20 @@ Required for new Resources delete functionality
 To prepare for the migration, deploy DIVA 3.1.0 and then execute the migration. Make sure your DIVA instance
 is not actively used in a production environment until the migration is completed to avoid potential inconsistencies.
 
-### With docker
+### Preparation
+
+We assume that DIVA 3.0.3 is already in use. First, the latest version must be deployed. You can simply download the latest
+DIVA distribution from [releases](https://github.com/FraunhoferISST/diva/releases) and follow our 
+[docker deployment guid](https://fraunhoferisst.github.io/diva-docs/deployment/).
+
+> It is not required to stop the running DIVA instance. Docker handles seamless update and deployment of new containers
+
+### Migrate with docker
 
 **Requirements**
 - Docker 20.10.x
 - Docker Compose 1.28.x
+- `.env` file in `docker/`
 
 Navigate to `docker/` and run:
 
@@ -43,8 +54,9 @@ docker-compose -f docker-compose.migration.yml up
 
 **Requirements**
 - Node 14.16
+- DIVA source code
 
-Navigate to `migration/`, install dependencies and run the migration script:
+In the DIVA source code from the repository navigate to `migration/`, install dependencies and run the migration script:
 
 >⚠️ Please note that you have to set the environment variables from your `.env` 
 >