doc: use sentence-style capitlaztion in template header

Make the level one header for all the HTML documents use consistent
capitalization style as the documentation itself.

PR-URL: https://github.com/nodejs/node/pull/37837
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

doc/template.html

@@ -24,7 +24,7 @@
     <div id="column1" data-id="__ID__" class="interior">
       <header>
         <div class="header-container">
-          <h1>Node.js __VERSION__ Documentation</h1>
+          <h1>Node.js __VERSION__ documentation</h1>
           <button class="theme-toggle-btn" id="theme-toggle-btn" title="Toggle dark mode/light mode" aria-label="Toggle dark mode/light mode" hidden>
             <svg xmlns="http://www.w3.org/2000/svg" class="icon dark-icon" height="24" width="24">
               <path fill="none" d="M0 0h24v24H0z" />