Tweak admin lookup template

templates/lookup.html

@@ -5,8 +5,10 @@
 <div id="container">
 <div style="margin-top:50px;">
 
+<p>Interact with an ActivityPub object via its URL or look for a user using <i>@user@domain.tld</i></p>
+
 <form id="lookup-form" method="GET">
- <input type="text" name="url" value="{{url or '' }}" placeholder="https://url-of-a-user-or-a-note.tld">
+<input type="text" name="url" value="{{url or '' }}">
 <input type="submit" value="Lookup">
 </form>