Copy edit rtos.md

Copy edit file, mostly for active voice and minor grammar nits.

Author: Amanda Butler

docs/reference/api/rtos/rtos.md

@@ -1,18 +1,16 @@
 <h2 id="rtos-api">RTOS overview</h2>
 
-The Arm Mbed RTOS APIs provides C++ APIs to manage RTOS objects like thread, synchronization objects and timer. It also provides interfaces for attaching application
-specific idle hook function and to read the tick count from OS. The Arm Mbed RTOS layer also handles RTOS errors and report them into Mbed-OS error handling system.
+Arm Mbed OS provides C++ APIs to manage RTOS objects such as thread, synchronization objects and timer. It also provides interfaces for attaching an application-specific idle hook function and to read the tick count from OS. The Arm Mbed RTOS layer also handles RTOS errors and reports them into the Mbed OS error handling system.
 
-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.
+You can find the Mbed RTOS code in the RTOS subdirectory of the `mbed-os` repository. Please see [the Doxygen](https://os-doc-builder.test.mbed.com/docs/development/mbed-os-api-doxy/group__rtos.html) for more information.
 
 #### RTOS Ticker
-Platforms using RTOS, including Mbed OS, need a mechanism for counting the time and scheduling tasks. This is usually done by a timer which generates periodic interrupts and is called system tick timer. 
-Under Mbed OS, we call this mechanism RTOS ticker.
 
-SysTick is a standard timer available on most Cortex-M cores. Its main purpose is to raise an interrupt with set frequency (usually 1ms). In addition, many Mbed OS platforms 
-implement timers as part of peripherals. Mbed OS supports using SysTick or the peripheral timers as RTOS ticker.
+Platforms using RTOS, including Mbed OS, need a mechanism for counting the time and scheduling tasks. They usually do this with system tick timer, a timer that generates periodic interrupts. In Mbed OS, we call this mechanism the RTOS ticker.
 
-Mbed OS platforms uses SysTick as the default RTOS ticker, but if you want to use one of the peripheral timers as your RTOS ticker you can do so by overriding the default SysTick timer. For example, see [Low Power Ticker](/docs/development/reference/low-power-ticker.html) on how to use external low power timer to perform power efficient timing operations that only requires millisecond accuracy.
+SysTick is a standard timer available on most Cortex-M cores. Its main purpose is to raise an interrupt with a set frequency (usually 1 ms). In addition, many Mbed OS platforms implement timers as part of peripherals. Mbed OS supports using SysTick or the peripheral timers as the RTOS ticker.
+
+Mbed OS platforms uses SysTick as the default RTOS ticker, but if you want to use one of the peripheral timers as your RTOS ticker, you can override the default SysTick timer. For example, see the [low power ticker](/docs/development/reference/low-power-ticker.html) documentation on how to use an external low power timer to perform power-efficient timing operations that only require millisecond accuracy.
 
 #### RTOS APIs
 
@@ -28,7 +26,7 @@ The RTOS APIs handle creation and destruction of threads in Arm Mbed OS 5, as we
 - [EventFlags](/docs/development/reference/eventflags.html): An event channel that provides a generic way of notifying other threads about conditions or events.
 - [Event](/docs/development/reference/event.html): The queue to store events, extract them and excute them later.
 - [ConditionVariable](/docs/development/reference/conditionvariable.html): The ConditionVariable class provides a mechanism to safely wait for or signal state changes.
-- [Kernel](/docs/development/reference/kernel.html): Kernel namespace implements functions to control or read RTOS information like tick count.
+- [Kernel](/docs/development/reference/kernel.html): The Kernel namespace implements functions to control or read RTOS information such as tick count.
 
 ##### Default timeouts
 
@@ -58,5 +56,5 @@ Each `Thread` can wait for signals and be notified of events:
 [![View code](https://www.mbed.com/embed/?url=https://os.mbed.com/teams/mbed_example/code/rtos_signals/)](https://os.mbed.com/teams/mbed_example/code/rtos_signals/file/476186ff82cf/main.cpp)
 
 ##### Status and Error codes
-The Arm Mbed RTOS layer handles RTOS errors and report them using Mbed-OS error handling system. See the list of error codes in [Error Handling](/docs/development/reference/error-handling.html)
-for more information on RTOS errors reported.
+
+The Arm Mbed RTOS layer handles RTOS errors and report them using the Mbed OS error handling system. Please see the list of error codes in the [error handling](/docs/development/reference/error-handling.html) documentation for more information on RTOS errors reported.