Changing boolean text in workflow email

Hello All,

 I am relatively new to Nintex Workflow 2010. 

I have a list with some boolean (yes/no) columns that are included in an email that is sent by a workflow. The fields appear as true/false when the email is sent, but I would rather see custom text i.e. Done for Yes and Not Done for No.

 Please could you help throw some pointers on how this can be achieved?

 Many thanks,

 Regards,

 Siva