Add CHANGELOG entry for keyUsage extension (#7139)

Author: eddyashton

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
   - The `js_generic` sample app is no longer a library installed at `/ccf/lib/libjs_generic.so`, it is now an executable installed at `/ccf/bin/js_generic`.
   - The `add_ccf_app` function in CMake now builds an executable rather than a library. The caller should provide a `main` function, and call `ccf::run()` from `include/ccf/run.h` to start the node (see `samples/apps/main.cpp` for a minimal example).
 - Application logging no longer traverses the ringbuffer. As current target platforms do not require distinct enclave and host components, what was previously "in-enclave" logging that was deferred via the ringbuffer can now be immediately sent to stdout.
+- CA certificates issued by CCF (ie - `service_cert.pem`) now include a `keyUsage` extension, to comply with RFC5280 (#7134).
 
 ### Dependencies