Add hint after instance field.

index.html

@@ -35,7 +35,7 @@
       {
         margin-left: 10ch;
       }
-      span.optional
+      span.hint
       {
         font-style: italic;
       }
@@ -132,6 +132,7 @@
     <form method="post" action="/add" enctype="multipart/form-data">
       <label for="instance">Instance:</label>
       <input type="text" id="instance" name="instance" placeholder="example.com" required>
+      <span class="hint">(Without the “https://”)</span>
       <br>
 
       <label for="tags">Tags:</label>
@@ -145,7 +146,7 @@
       <!-- <input type="button" id="add_receipt" value="➕" disabled> -->
       <br>
 
-      <label for="screenshot1">Screenshots:</label><span class="optional">(optional)</span>
+      <label for="screenshot1">Screenshots:</label><span class="hint">(optional)</span>
       <br>
       <input type="file" id="screenshot1" name="screenshots[]" accept="image/*">
       <br>