fix(docs): close hero div so why section is not nested

- missing </div> after hero-terminal pulled #why into .hero
- section-alt full-bleed border rendered as empty band under terminal

Author: debugtalk

docs/index.html

@@ -181,6 +181,8 @@ <h1 data-i18n="hero.title" data-i18n-html>
 <span class="prompt">$</span> curl -fsSL piex.dev/scripts/install.sh | bash</pre>
         </div>
 
+      </div>
+
       <section id="why" class="section-alt">
         <div class="section-header anim-fade">
           <div class="section-heading">