Rename master references to main
## Overview
-The AWS IoT Device SDK for Embedded C (C-SDK) is a collection of C source files under the [MIT open source license](LICENSE) that can be used in embedded applications to securely connect IoT devices to [AWS IoT Core](https://docs.aws.amazon.com/iot/latest/developerguide/what-is-aws-iot.html). It contains MQTT client, HTTP client, JSON Parser, AWS IoT Device Shadow, AWS IoT Jobs, and AWS IoT Device Defender libraries. This SDK is distributed in source form, and can be built into customer firmware along with application code, other libraries and an operating system (OS) of your choice. These libraries are only dependent on standard C libraries, so they can be ported to various OS's - from embedded Real Time Operating Systems (RTOS) to Linux/Mac/Windows. You can find sample usage of C-SDK libraries on POSIX systems using OpenSSL (e.g. [Linux demos](demos) in this repository), and on [FreeRTOS](https://github.com/FreeRTOS/FreeRTOS/) using mbedTLS (e.g. [FreeRTOS demos](https://github.com/FreeRTOS/FreeRTOS/tree/master/FreeRTOS-Plus/Demo) in [FreeRTOS](https://github.com/FreeRTOS/FreeRTOS/) repository).
+The AWS IoT Device SDK for Embedded C (C-SDK) is a collection of C source files under the [MIT open source license](LICENSE) that can be used in embedded applications to securely connect IoT devices to [AWS IoT Core](https://docs.aws.amazon.com/iot/latest/developerguide/what-is-aws-iot.html). It contains MQTT client, HTTP client, JSON Parser, AWS IoT Device Shadow, AWS IoT Jobs, and AWS IoT Device Defender libraries. This SDK is distributed in source form, and can be built into customer firmware along with application code, other libraries and an operating system (OS) of your choice. These libraries are only dependent on standard C libraries, so they can be ported to various OS's - from embedded Real Time Operating Systems (RTOS) to Linux/Mac/Windows. You can find sample usage of C-SDK libraries on POSIX systems using OpenSSL (e.g. [Linux demos](demos) in this repository), and on [FreeRTOS](https://github.com/FreeRTOS/FreeRTOS/) using mbedTLS (e.g. [FreeRTOS demos](https://github.com/FreeRTOS/FreeRTOS/tree/main/FreeRTOS-Plus/Demo) in [FreeRTOS](https://github.com/FreeRTOS/FreeRTOS/) repository).
For the latest release of C-SDK, please see the section for [Releases and Documentation](#releases-and-documentation).
