Default styling for bullet point lists

I just noticed that https://datasette.io/content/recent_releases (which uses `datasette-render-markdown`) is missing its bullet points:

<img width="864" alt="content__recent_releases__399_rows" src="https://user-images.githubusercontent.com/9599/101970823-95b0bb80-3be1-11eb-9512-9274cef64cf3.png">
