Added ENABLE_CONVERSIONS environment variable (#635)

docker-compose.yml

@@ -29,6 +29,9 @@ services:
 
             ENABLED_LINKED_FILE_TYPES: 'url,project_file'
 
+            # Enables Thumbnail generation using ImageMagick
+            ENABLE_CONVERSIONS: 'true'
+
             ## Set for SSL via nginx-proxy
             #VIRTUAL_HOST: 103.112.212.22