--- a/register.html	Tue Apr 12 15:10:58 2016 +0800
+++ b/register.html	Tue Apr 12 16:07:56 2016 +0800
@@ -85,6 +85,13 @@
           <label for="avatar" class="uk-form-label">Avatar</label>
           <div class="uk-form-controls">
             <input id="avatar" type="file" accept="image/*" value="">
+            <p>A good avatar:</p>
+            <ul>
+              <li>has width and height between 32 and 96 pixels</li>
+              <li>ideally is a square image</li>
+              <li>is less than 64k in size</li>
+              <li>is in a widespread format (png, gif or jpeg)</li>
+            </ul>
           </div>
         </div>
         <div class="uk-form-row">