Document IPNetwork/cidr breaking change

Author: roji

conceptual/EFCore.PG/release-notes/9.0.md

@@ -85,6 +85,10 @@ If your application passes an NpgsqlDataSource to `UseNpgsql`, it also needs to
 
 See the [enum documentation](../mapping/enum.md) for more information.
 
+### PostgreSQL `cidr` is now mapped to .NET `IPNetwork` by default.
+
+When scaffolding a table that contains a `cidr` column, a .NET [`IPNetwork`](https://learn.microsoft.com/dotnet/api/system.net.ipnetwork) will be scaffolded instead of the previous `NpgsqlCidr`.
+
 ## Contributors
 
 A big thank you to all the following people who contributed to the 9.0 release!