A tag is a short description of a transaction,
 which lets you categorize your expenses in a flexible manner. 
 There are no fixed set of tags, you can just create any tag you want.
 You can attach multiple tags to the same transaction.
 Example: If you went out for coffee with your friends John and
 Mary and you paid by your credit card, you can tag the transaction
 with "coffee" as well as "credit card".