fix: Update JSONRPCTransportConfig option in README (#249)

# Description

Thank you for opening a Pull Request!
Before submitting your PR, there are a few things you can do to make
sure it goes smoothly:

- [x] Follow the [`CONTRIBUTING` Guide](../CONTRIBUTING.md).
- [x] Make your Pull Request title in the
<https://www.conventionalcommits.org/> specification.
- Important Prefixes for
[release-please](https://github.com/googleapis/release-please):
- `fix:` which represents bug fixes, and correlates to a
[SemVer](https://semver.org/) patch.
- `feat:` represents a new feature, and correlates to a SemVer minor.
- `feat!:`, or `fix!:`, `refactor!:`, etc., which represent a breaking
change (indicated by the `!`) and will result in a SemVer major.
- [x] Ensure the tests pass
- [x] Appropriate READMEs were updated (if necessary)

Author: fjuma

README.md

@@ -316,9 +316,9 @@ Different transport protocols can be configured with specific settings using spe
 
 ##### JSON-RPC Transport Configuration
 
-For the JSON-RPC transport, if you'd like to use the default `JdkA2AHttpClient`, no additional
-configuration is needed. To use a custom HTTP client implementation, simply create a `JSONRPCTransportConfig`
-as follows:
+For the JSON-RPC transport, to use the default `JdkA2AHttpClient`, provide a `JSONRPCTransportConfig` created with its default constructor.
+
+To use a custom HTTP client implementation, simply create a `JSONRPCTransportConfig` as follows:
 
 ```java
 // Create a custom HTTP client