Fix bullet point indicators

Author: Jud Dagnall

visidata/guides/ColumnsGuide.md

@@ -53,6 +53,6 @@ the current column width. Row height adjustments can also be combined with
 column width changes.
 
 - {help.commands.toggle_multiline}
-_ {help.commands.resize_height_input}
-_ {help.commands.resize_height_max}
+- {help.commands.resize_height_input}
+- {help.commands.resize_height_max}