Copy edit rtc.md

Copy edit for active voice, branding and minor grammar issues.

Author: Amanda Butler

docs/contributing/rtc.md

@@ -1,41 +1,40 @@
-# RTC HAL API
+## RTC HAL API
 
-The RTC HAL API provides a low level interface to the Real Time Counter (RTC) of a target.
+The RTC HAL API provides a low-level interface to the Real Time Counter (RTC) of a target.
 
-## Assumptions
+### Assumptions
 
-### Defined behavior
+#### Defined behavior
 
-- The function `rtc_init` is safe to call repeatedly
-- RTC accuracy is at least 10%
-- `Init`/`free` doesn't stop RTC from counting
-- Software reset doesn't stop RTC from counting
-- Sleep modes don't stop RTC from counting
-- Shutdown mode doesn't stop RTC from counting
+- The function `rtc_init` is safe to call repeatedly.
+- RTC accuracy is at least 10%.
+- `Init`/`free` doesn't stop RTC from counting.
+- Software reset doesn't stop RTC from counting.
+- Sleep modes don't stop RTC from counting.
+- Shutdown mode doesn't stop RTC from counting.
 
-### Undefined behavior
+#### Undefined behavior
 
-- Calling any function other than `rtc_init` before the initialization of the RTC
+- Calling any function other than `rtc_init` before the initialization of the RTC.
 
-### Potential bugs
+#### Potential bugs
 
-- Incorrect overflow handling
-- Glitches due to ripple counter
+- Incorrect overflow handling.
+- Glitches due to ripple counter.
 
-## Implementing the RTC API
+### Implementing the RTC API
 
-RTC HAL API is located in [hal/rtc_api.h](). Following functions need to be implemented to support RTC:
+RTC HAL API is in [hal/rtc_api.h](). You need to implement the following functions to support RTC:
 
+To enable sleep support in Mbed OS, you need to add the `RTC` label in the `device_has` option of the target's section in the `targets.json` file.
 
-To enable sleep support in mbed OS `RTC` label needs to be added in `device_has` option of target's section in `targets.json` file.
-
-## Testing
+### Testing
 
 The [RTC HAL API test suite]() validates:
 
-- `rtc_init` is safe to call repeatedly - Verified by test `rtc_init_test`
-- `Init`/`free` doesn't stop RTC from counting - Verified by test `rtc_persist_test`
-- Software reset doesn't stop RTC from counting - Verified by `rtc_reset_test`
-- Sleep modes don't stop RTC from counting - Verified by `rtc_sleep_test`
-- Overflow handling - Verified by `rtc_range_test`
-- No backward glitches - Verified by `rtc_glitch_test`
+- `rtc_init` is safe to call repeatedly - Verified by test `rtc_init_test`.
+- `Init`/`free` doesn't stop RTC from counting - Verified by test `rtc_persist_test`.
+- Software reset doesn't stop RTC from counting - Verified by `rtc_reset_test`.
+- Sleep modes don't stop RTC from counting - Verified by `rtc_sleep_test`.
+- Overflow handling - Verified by `rtc_range_test`.
+- No backward glitches - Verified by `rtc_glitch_test`.