I'm always confused when using `decimal` in a Rails migration. Normally I need to store a value that has 2 or 3 numbers behind the comma (or dot), or decimals.
Let's say you have a `Product` model with a `discount_percentage` attribute. This attribute is currently an integer, only allowing non-decimal values. To allow 2 digit decimal values (e.g. `12.54`), you can mak the following migration: