Update README.md with information about the new test

Author: terasakisatoshi

README.md

@@ -181,6 +181,7 @@ Key files to study:
 - **Bug Fix**: Fixed an issue where changing the seed value in the configuration file wasn't properly affecting the output image. The bug was in the `render_from_config` function where the RNG state wasn't being properly managed.
 - **Bug Fix**: Fixed color inconsistency between the basic example and the main program. Now both methods produce the same colors for the same seed.
 - **Change**: Updated the default seed value to 99 throughout the codebase.
+- **Test**: Added a test to verify that the images generated by the basic example and the main program are identical.
 
 ## Performance