[cli] add README for TCP CLI tool (#6857)
[cli] add README for TCP CLI tool (#6857)


srickardti/openthread,jwhui/openthread,srickardti/openthread,openthread/openthread,abtink/openthread,abtink/openthread,jwhui/openthread,jwhui/openthread,openthread/openthread,abtink/openthread,jwhui/openthread,srickardti/openthread,openthread/openthread,openthread/openthread,srickardti/openthread,abtink/openthread