Update README.md to link to the set of release notes

Instead of referencing a specific release version here, thus negating the need to update this readme for every minor release.

Author: adbridge

README.md

@@ -5,10 +5,9 @@ mbed OS is an open-source embedded operating system designed specifically for th
 mbed OS accelerates the process of creating a connected product by providing a platform operating system that includes robust security foundations, standards based communication capabilities, built-in cloud management services, and drivers for sensors, I/O devices and connectivity. mbed OS is built as a modular, configurable software stack so that you can readily customize it to the device you're developing for, and reduce memory requirements by excluding unnecessary software components.
 
 ## Current release
- 
-Our current release series is mbed OS 5.2:
 
-- [Release Note](https://docs.mbed.com/docs/mbed-os-release-notes/en/latest/5_2/release_note/)
+The current release, along with a selection of previous versions are detailed here:
+[Release Notes](https://docs.mbed.com/docs/mbed-os-release-notes/en/latest/)
 
 ## Getting Started for Developers