Add currentUser template func

templates/tailwind.gohtml

@@ -16,12 +16,15 @@
           <a class="text-base font-semibold hover:text-blue-100 pr-8" href="/faq">FAQ</a>
         </div>
         <div class="space-x-4">
+         {{if currentUser }}
           <form action="/signout" method="post" class="inline pr-4">
             {{csrfField}}
             <button type="submit">Sign out</button>
           </form>
+         {{else}}
           <a href="/signin">Sign in</a>
           <a href="/signup" clss="px-4 py-2 bg-blue-700 hover:bg-blue-600 rounded">Sign up</a>
+         {{end}}
         </div>
       </nav>
     </header>