Add breaking change notice for preserve_client_ip default behavior

Signed-off-by: speruri <surya.srikar.peruri@zalando.de>

Author: speruri

README.md

@@ -61,6 +61,7 @@ Version `v0.20` adds support for NLB target group attributes:
   - Preserves client IP address in NLB target group connections
   - Defaults to true, matching AWS NLB default behavior
   - Set to false to override and disable this feature
+  - **Breaking change**: Previously this attribute was not explicitly set. Updating to v0.20 will set `preserve_client_ip.enabled=true` on all NLB target groups. For setups that require it disabled, use `--nlb-preserve-client-ip=false`
 
 These attributes are only applied to Network Load Balancer target groups. Application Load Balancers are not affected.