Disable "please select"

static/crossroad.html

@@ -91,7 +91,7 @@ Unchecking this is not recommended, and this option only exists for exceptional
                     <label for="instanceSoftware">Instance software</label>
                     <br>
                     <select id="instanceSoftware" type="text" name="instanceSoftware" required>
-                        <option value="">(Please select)</option>
+                        <option value="" disabled>(Please select)</option>
                     </select>
                 </div>
                 <div class="half-width flex-row-reverse">