add further clarity re: conventions

snake_case is also an option - so adding that in.

rails-migrations.md

@@ -6,7 +6,10 @@ category: Rails
 ### Automatically make migrations
 
     $ rails generate migration RemovePartNumberFromProducts part_number:string
+    $ rails generate migration remove_part_number_from_products part_number # rails assumes string if not type given
+    
     $ rails generate migration AddNameToWidgets name:string
+    $ rails generate migration add_name_to_widgets name:string
 
 ### Run migrations