docs: add extract cookie example

apps/docs/docs/editor/blocks/logic/set-variable.md

@@ -50,3 +50,20 @@ window.location.href
 It will not give you the parent URL if you embed the bot on your site.
 A more bulletproof option is to pass the URL as a hidden variable in the embed code options. You can find an example [here](/embed/html-javascript#additional-configuration).
 :::
+
+## Extract a cookie
+
+This code allows you to extract the value of a cookie called "my_cookie":
+
+```js
+const getCookie = (name) => {
+  const value = `; ${document.cookie}`
+  const parts = value.split(`; ${name}=`)
+  if (parts.length === 2) return parts.pop().split(';').shift()
+  return 'not found'
+}
+
+return getCookie('my_cookie')
+```
+
+As you can see the code can also be multi-line. The Set variable block will get the value following the `return` statement.