add hints to various sections in /user/site-settings.html template.

These are just blocks of <p> tags to help explain what the various settings do
in each section.

templates/user/site-settings.html

@@ -169,7 +169,12 @@
 
     <hr>
     
-    <h2>Nav. Menu</h2>
+    <h2>Navigation Menu</h2>
+    <p class="be-gui-form-hint">
+        This is the list of links at the top of the page and is viewable by
+        everyone. The nav. menu can only consist of 'Pages', no 'Archive
+        Entries' can be selected for this menu.
+    </p>
     <form class="be-gui-form"
           action="/site-settings/update-nav-menu"
           method="post">
@@ -206,7 +211,8 @@
     
     <h2>Favicon</h2>
     <p class="be-gui-form-hint">
-        A Favicon is the little image in the browser tab.
+        A Favicon is the little image in the browser tab. You might need to
+        press 'Shift + F5' if you cannot see the new file.
     </p>
     <form class="be-gui-form"
           action="/site-settings/update-favicon"