autodoc: show binding in lowercase

<S-s> is not bound and shortcuts popup already use lowercase.

Author: McSinyx

lib/docs/index.html

@@ -633,7 +633,7 @@ <h2><span>Zig Version</span></h2>
         <div class="wrap">
           <section class="docs">
             <div style="position: relative">
-              <span id="searchPlaceholder"><kbd>S</kbd> to search, <kbd>?</kbd> for more options</span>
+              <span id="searchPlaceholder"><kbd>s</kbd> to search, <kbd>?</kbd> for more options</span>
               <input type="search" class="search" id="search" autocomplete="off" spellcheck="false" disabled>
             </div>
             <p id="status">Loading...</p>