Update placeholder and validation

src/main/resources/templates/admin.html

@@ -392,7 +392,7 @@
                         <textarea
                             class="text-input"
                             id="custom-asset-code"
-                            placeholder="function init({ surface, assets, channel }) {&#10;&#10;}&#10;&#10;function tick() {&#10;&#10;}"
+                            placeholder="exports.init = ({ surface, assets, channel }) => {&#10;&#10;};&#10;&#10;exports.tick = () => {&#10;&#10;};"
                             rows="25"
                             required
                         ></textarea>