Update [ListTextAttribute] docs

[meghanmae]

When I get this error message, my first step is to look up [ListTextAttribute], because I just copy-paste the name from the error message. It would be nice to be able to easily search the fully qualified attribute name rather than having to shorten it to the C# conventional name [ListText]

** Failure: StormingTheCastle.Data.Models.MyModel.MyModelProperty: The target object for the property has no discernible display text. Add a [ListTextAttribute] to one of its properties.
[e:15.860] Model validation failed. Exiting.