Update MISRA.md with explanation about 5.6 flagging. (#1265)
Update MISRA.md with explanation about 5.6 flagging. (#1265)

Co-authored-by: SarenaAWS <93d3d3d909f752df01ee3ccf256948db4022e71f@users.noreply.github.com>
aws/aws-iot-device-sdk-embedded-C,aws/aws-iot-device-sdk-embedded-C,aws/aws-iot-device-sdk-embedded-C