added doc

database/doc.go

@@ -13,3 +13,15 @@ Example usage:
 	go dba.Run(ctx)
 
 */
+
+/*
+   Transactor Example:
+
+   func insert(ctx context.Context, db *sql.DB) error{
+	// SQL HERE
+   }
+
+   ...
+
+   dba.ActionChan <- db.WithTransaction(insert)
+*/