Clarify build instructions for Ubuntu (#1656)
Clarify build instructions for Ubuntu (#1656)

* Clarify build instructions for Ubuntu

* Update README.md

Co-authored-by: Oscar Michael Abrina <d3a96674f6acc9688c9e78d3dd3a4f7580b23860@amazon.com>

Co-authored-by: Oscar Michael Abrina <d3a96674f6acc9688c9e78d3dd3a4f7580b23860@amazon.com>
aws/aws-iot-device-sdk-embedded-C,aws/aws-iot-device-sdk-embedded-C,aws/aws-iot-device-sdk-embedded-C