[nrf52840] update documentation and fix broken link (#3986)
[nrf52840] update documentation and fix broken link (#3986)

Signed-off-by: Duda, Lukasz <714d933c7fb37343dcea36d8abaf85e065f4c5bc@nordicsemi.no>
chshu/openthread,abtink/openthread,abtink/openthread,bukepo/openthread,lanyuwen/openthread,openthread/openthread,openthread/openthread,turon/openthread,lanyuwen/openthread,chshu/openthread,srickardti/openthread,chshu/openthread,srickardti/openthread,bukepo/openthread,chshu/openthread,librasungirl/openthread,bukepo/openthread,librasungirl/openthread,jwhui/openthread,jwhui/openthread,abtink/openthread,jwhui/openthread,lanyuwen/openthread,turon/openthread,lanyuwen/openthread,jwhui/openthread,abtink/openthread,chshu/openthread,turon/openthread,librasungirl/openthread,lanyuwen/openthread,bukepo/openthread,openthread/openthread,openthread/openthread,srickardti/openthread,librasungirl/openthread,lanyuwen/openthread,chshu/openthread,srickardti/openthread,turon/openthread