chore(ec2): update vpc README with vpc lookup method (#34544)

### Issue # (if applicable)

### Reason for this change

We recommend to use cross stack reference but does not provide workaround when fail due to cross stack reference issue.

### Description of changes

Adding a readme to explain

### Describe any new or updated permissions being added




### Description of how you validated changes



### Checklist
- [ ] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

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

Author: GavinZZ

packages/aws-cdk-lib/aws-ec2/README.md

@@ -608,6 +608,14 @@ instance around:
 
 [sharing VPCs between stacks](test/integ.share-vpcs.lit.ts)
 
+> Note: If you encounter an error like "Delete canceled. Cannot delete export ..."
+> when using a cross-stack reference to a VPC, it's likely due to CloudFormation
+> export/import constraints. In such cases, it's safer to use Vpc.fromLookup()
+> in the consuming stack instead of directly referencing the VPC object, more details
+> is provided in [Importing an existing VPC](#importing-an-existing-vpc). This
+> avoids creating CloudFormation exports and gives more flexibility, especially
+> when stacks need to be deleted or updated independently.
+
 ### Importing an existing VPC
 
 If your VPC is created outside your CDK app, you can use `Vpc.fromLookup()`.