encourage attribution

lib/views/index.html.ejs

@@ -148,6 +148,17 @@
           You can append <code>.png</code> or any other file extension to the URL path if you like to, but all images are PNG.
         </p>
 
+        <section id="meta-attribution">
+          <h3><a href="#meta-attribution">Attribution</a></h3>
+          <p>
+            Attribution is <strong>encouraged</strong> but not required.<br>
+            If you want to show some support for this (free!) site, place a notice like this somewhere:
+            <div class="code">
+              Thank you to &lt;a href="https://crafatar.com"&gt;Crafatar&lt;/a&gt; for providing avatars.
+            </div>
+          </p>
+        </section>
+
         <section id="meta-parameters">
           <h3><a href="#meta-parameters">URL Parameters</a></h3>
           <p>