Copy edit README.md

Make minor copy edits for comma use and consistent capitalization across documents.

Author: Amanda Butler

README.md

@@ -16,20 +16,20 @@
 [mbed-waffle]: https://waffle.io/ARMmbed/mbed-os
 [mbed-waffle-svg]: https://badge.waffle.io/ARMmbed/mbed-os.svg?columns=all
 
-Arm Mbed OS is an open source embedded operating system designed specifically for the "things" in the Internet of Things. It includes all the features you need to develop a connected product based on an Arm Cortex-M microcontroller, including security, connectivity, an RTOS, and drivers for sensors and I/O devices.
+Arm Mbed OS is an open source embedded operating system designed specifically for the "things" in the Internet of Things. It includes all the features you need to develop a connected product based on an Arm Cortex-M microcontroller, including security, connectivity, an RTOS and drivers for sensors and I/O devices.
 
 Mbed OS provides a platform that includes:
 * Security foundations.
 * Cloud management services.
 * Drivers for sensors, I/O devices and connectivity. 
 
-## Release Notes
-The [release notes](https://os.mbed.com/releases) detail the current release and you can also find information about previous versions.
+## Release notes
+The [release notes](https://os.mbed.com/releases) detail the current release. You can also find information about previous versions.
 
-## Getting Started for Developers
+## Getting started for developers
 
 We have a [developer webiste](https://os.mbed.com) for asking questions, engaging with others, finding information on boards and components, using an online IDE and compiler, reading the documentation and learning about what's new and what's coming next in Mbed OS.
 
-## Getting Started for Contributors
+## Getting started for contributors
 
 We also have a [contributing and publishing guide](https://os.mbed.com/contributing/) that covers licensing, contributor agreements and style guidelines.