text in power or indice

the _config.yml (site and theme) doesn't accept markdown syntax.
How to write a text in power or indice (e.g in theme.about) ?

[tomap]

You could write HTML directly, and change the rendering of about in your theme to not be htmlencoded:
<%- theme.about %> instead of <%= theme.about %>

Be sure to check all instances of theme.about (of config.about )