docs(certificatemanager): Fix typo 'ExampelNet' -> 'ExampleNet' (#13319)

Fixing a small typo in the aws-certificatemanager README.


----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/aws-certificatemanager/README.md

@@ -68,7 +68,7 @@ When working with multiple domains, use the `CertificateValidation.fromDnsMultiZ
 const exampleCom = new route53.HostedZone(this, 'ExampleCom', {
   zoneName: 'example.com',
 });
-const exampleNet = new route53.HostedZone(this, 'ExampelNet', {
+const exampleNet = new route53.HostedZone(this, 'ExampleNet', {
   zoneName: 'example.net',
 });