update CHANGELOG w/ link to PR

Author: tobz

Diff for: CHANGELOG.md

@@ -12,7 +12,7 @@ adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 - Fixed an issue with the monotonic clock for macOS/iOS where it would undermeasure time compared to
   what would be measured by `std::time::Instant` due to using a clock source that did not account
-  for device sleep.
+  for device sleep. ([#97](https://github.com/metrics-rs/quanta/pull/97))
 
 ## [0.12.1] - 2023-10-31