created docstring for set_button_amount()

lib/gui_lite.py

@@ -318,6 +318,8 @@ class MiniWindow(QDialog):
             self.amount_input.setText("")
 
     def check_button_status(self):
+        """Check that the bitcoin address is valid and that something
+        is entered in the amount before making the send button clickable."""
         if (self.address_input.property("isValid") == True and
             len(self.amount_input.text()) > 0):
             self.send_button.setDisabled(False)