chore: add docs for dc file

docker-compose.yml

@@ -1,3 +1,6 @@
+# The docker-compose.yml file is __only__ used for local development.
+# This means that changes to this file will not affect cloud deployments in any way.
+# Read more at https://docs.divio.com/reference/docker-docker-compose/
 services:
   web:
     build: .
@@ -7,9 +10,12 @@ services:
       - '.:/app:rw'
       - './data:/data:rw'
       - 'node_modules:/app/node_modules'
+    # We are using the .env file to store environment variables locally.
     env_file: '.env'
     links:
       - 'database_default'
+    # The following command is used to start the local development server.
+    # Removing this line will mimic the deployment behaviour on Divio Cloud.
     command: 'npm run develop'
 
   database_default: