docs: fix opts argument and embed code sandbox

docs/pages/docs/getting-started.mdx

@@ -30,19 +30,19 @@ Then you can create your own validators such as validators for `email`, `minLeng
 </Callout>
 
 ```js
-const email = string.create((value: string, { message }: { message?: string } = {}) => {
+const email = string.create((value: string, opts: { message?: string } = {}) => {
   if (!value.includes("@"))
-    throw new Error(message ?? "Invalid email");
+    throw new Error(opts.message ?? "Invalid email");
 });
 
 const minLength = string.create((value: string, minLength: number, opts: { message?: string } = {}) => {
   if (value.length < minLength)
-    throw new Error(message ?? `Must be at least ${minLength} characters`);
+    throw new Error(opts.message ?? `Must be at least ${minLength} characters`);
 });
 
 const maxLength = string.create((value: string, maxLength: number, opts: { message?: string } = {}) => {
   if (value.length > maxLength)
-    throw new Error(message ?? `Must be at most ${maxLength} characters`);
+    throw new Error(opts.message ?? `Must be at most ${maxLength} characters`);
 });
 ```
 
@@ -66,3 +66,7 @@ try {
   console.log(error.message); // Must be at least 3 characters
 }
 ```
+
+## Code Sandbox Example
+
+<iframe style={{ border: '1px solid rgba(0, 0, 0, 0.1)', borderRadius: '2px' }} width="800" height="450" src="https://codesandbox.io/p/sandbox/cevali-example-k7ttt9?embed=1" allowfullscreen></iframe>