docs: add links to custom AWS KMS client configuration examples in examples readme (#269)

* docs: add links to client supplier examples in examples readme

* docs: change client supplier examples framing in readme from implementation details to use-case

Author: mattsb42-aws

examples/README.md

@@ -46,6 +46,10 @@ We start with AWS KMS examples, then show how to use other wrapping keys.
         * [with keyrings](./src/keyring/aws_kms/discovery_decrypt_with_preferred_regions.py)
     * How to reproduce the behavior of an AWS KMS master key provider
         * [with keyrings](./src/keyring/aws_kms/act_like_aws_kms_master_key_provider.py)
+    * How to use AWS KMS clients with custom configuration
+        * [with keyrings](./src/keyring/aws_kms/custom_kms_client_config.py)
+    * How to use different AWS KMS client for different regions
+        * [with keyrings](./src/keyring/aws_kms/custom_client_supplier.py)
 * Using raw wrapping keys
     * How to use a raw AES wrapping key
         * [with keyrings](./src/keyring/raw_aes/raw_aes.py)