add new doc

Author: kmurphypolygon

docs/cdk/how-to/migration/7-8.md

@@ -83,6 +83,8 @@ nav:
               - Start services: cdk/get-started/deploy-rollup/start-services.md
         - Connect to CDK testnet: cdk/get-started/connect-testnet.md
       - How to:
+        - Migrate:
+          - Fork 7 to 8: ckd/how-to/migration-guides/7-8.md
         - Use a native token: cdk/how-to/use-native-token.md
         - Manage allowlists with policies: cdk/how-to/manage-policies.md
         - Quickly test a running stack: cdk/how-to/quick-test-stack.md