Fix outdated logging documentation link in README (#444)

The logging section in the README linked to the old C++ driver
documentation instead of the cpp-rs-driver docs.

## Changes

- Updated logging docs URL from
`https://cpp-driver.docs.scylladb.com/master/topics/logging/index.html`
to
`https://cpp-rs-driver.docs.scylladb.com/stable/topics/observability/logging.html`

## Pre-review checklist

- [ ] I have split my patch into logically separate commits.
- [x] All commit messages clearly explain what they change and why.
- [x] PR description sums up the changes and reasons why they should be
introduced.
- [ ] I have implemented Rust unit tests for the features/changes
introduced.
- [ ] I have enabled appropriate tests in `Makefile` in
`{SCYLLA,CASSANDRA}_(NO_VALGRIND_)TEST_FILTER`.
- [ ] I added appropriate `Fixes:` annotations to PR description.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: wprzytula <59482568+wprzytula@users.noreply.github.com>

Author: Copilot

README.md

@@ -111,7 +111,7 @@ int main(int argc, char* argv[]) {
 # Logging
 ___
 
-The logging API and implementation are compatible with the C++ driver, for more details please refer to the [logging documentation](https://cpp-driver.docs.scylladb.com/master/topics/logging/index.html).
+The logging API and implementation are compatible with the C++ driver, for more details please refer to the [logging documentation](https://cpp-rs-driver.docs.scylladb.com/stable/topics/observability/logging.html).
 As the `tracing` framework is used under the hood to instrument the collection of logs from the Rust driver and the scylla-rust-wrapper,
 the logging level and callback are passed through a custom event subscriber which is globally set as default when `cass_log_set_level` is called.
 So, `cass_log_set_level` *must* be called only once as subsequent attempts trying to modify the globally set event subscriber will be ignored.