How do I add small text below an answer?

I sometimes see quizzes where you enter the answer, and it shows up in the table, except below there is some more small text.

An example would be in https://www.jetpunk.com/user-quizzes/91108/all-cities-in-china-with-population-of-1-million. When I insert "Guangzhou," it will say "(incl. Shenzhen)" in small text at the bottom. How do you do that?