Fix hero text visibility in light theme

Remove hardcoded text-white and hero-text classes from the hero
section; default body colour adapts correctly to both light and
dark themes.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: xoofx

site/readme.md

@@ -4,7 +4,7 @@ layout: simple
 og_type: website
 ---
 
-<section class="text-center py-5 text-white hero-text">
+<section class="text-center py-5">
   <div class="container">
     <h1 class="fw-bold display-5">
       <span class="c64-text">XenoAtom</span>