Fix link in rtos.md

Fix broken link.

Author: Amanda Butler

docs/api/rtos/rtos.md

@@ -2,7 +2,7 @@
 
 The Mbed OS RTOS capabilities include managing objects such as threads, synchronization objects and timers. It also provides interfaces for attaching an application-specific idle hook function, reads the OS tick count and implements functionality to report RTOS errors.
 
-The code of the Mbed RTOS can be found in the [`mbed-os`](https://github.com/ARMmbed/mbed-os) repository, in the [RTOS subdirectory](https://github.com/ARMmbed/mbed-os/blob/master/rtos). See [the Doxygen](../mbed-os-api-doxy/group__rtos.html) for more information.
+The code of the Mbed RTOS can be found in the [`mbed-os`](https://github.com/ARMmbed/mbed-os) repository, in the [RTOS subdirectory](https://github.com/ARMmbed/mbed-os/blob/master/rtos). See [the Doxygen](../mbed-os-api-doxy/group__rtos-public-api.html) for more information.
 
 ## Memory considerations