fixed brand-link in docs

docs/_includes/sidebar.html

   <aside class="main-sidebar sidebar-dark-primary elevation-4">
-    <a href="index3.html" class="brand-link logo-switch">
+    <a href="{{'index.html' | relative_url}}" class="brand-link logo-switch">
       <img src="{{'assets/img/logo-xs.png' | relative_url}}" alt="AdminLTE Docs Logo Small" class="brand-image-xl logo-xs">
       <img src="{{'assets/img/logo-xl.png' | relative_url}}" alt="AdminLTE Docs Logo Large" class="brand-image-xs logo-xl" style="left: 12px">
     </a>