Update README with LTS information (#79)

Author: aggarw13

README.md

@@ -6,6 +6,8 @@ This library has gone through code quality checks including verification that no
 
 See memory requirements for this library [here](https://docs.aws.amazon.com/embedded-csdk/202012.00/lib-ref/libraries/standard/coreJSON/docs/doxygen/output/html/index.html#json_memory_requirements).
 
+**coreJSON v3.0.0 [source code](https://github.com/FreeRTOS/coreJSON/tree/v3.0.0/source) is part of the [FreeRTOS 202012.00 LTS](https://github.com/FreeRTOS/FreeRTOS-LTS/tree/202012.00-LTS) release.**
+
 ## Reference example
 
 ```c