Add a section for plugins in Sail documentation

Author: elnurvl

sail.md

@@ -616,7 +616,7 @@ class YourSailPluginProvider extends ServiceProvider
 
                 return str_replace('REDIS_HOST=127.0.0.1', "REDIS_HOST=redis", $environment);
             },
-            default: true,
+            isDefault: true,
         )->setBaseTemplate('path-to-app-service.stub');
     }
 }
@@ -642,8 +642,6 @@ custom-service:
   image: custom/service:latest
   ports:
     - "8080:8080"
-  volumes:
-    - custom-service-data:/data
   networks:
     - sail
   depends_on: