Fix phrasing in rtos.md

Update phrasing as requested.

Author: Amanda Butler

docs/reference/api/rtos/rtos.md

@@ -1,6 +1,6 @@
 <h2 id="rtos-api">RTOS overview</h2>
 
-The Mbed OS RTOS provides C++ APIs to manage 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 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/tree/master/rtos). See [the Doxygen](https://os-doc-builder.test.mbed.com/docs/development/mbed-os-api-doxy/group__rtos.html) for more information.