Use 8 bytes payload as reference throughput value in README

8 bytes payload is the reference payload size when measuring throughput. It would be hence good to update the value on the README.

Author: Mallets

README.md

@@ -137,7 +137,7 @@ The `z_querier` should continuously send queries and receive replies from `z_que
 ```
 
 ```bash
-./z_pub_thr_cpp 1024
+./z_pub_thr_cpp 8
 ```
 
 After 30-40 seconds delay the `z_sub_thr` will start to show the throughput measure results.
@@ -182,4 +182,4 @@ Instruction how to build documentation locally is at [docs/README.md].
 [find_package]: https://cmake.org/cmake/help/latest/command/find_package.html
 [FetchContent]: https://cmake.org/cmake/help/latest/module/FetchContent.html
 [zenoh-cpp.readthedocs.io]: https://zenoh-cpp.readthedocs.io
-[docs/README.md]: https://github.com/eclipse-zenoh/zenoh-cpp/blob/main/docs/README.md
+[docs/README.md]: https://github.com/eclipse-zenoh/zenoh-cpp/blob/main/docs/README.md