samples: mgmt: Expand smp_svr sample documentation
samples: mgmt: Expand smp_svr sample documentation

Expand the contents of the smp_svr sample documentation so that it
covers all steps needed to perform DFU over BLE.

Signed-off-by: Carles Cufi <853081dc8dca4fe6a7e3c984752718b5db36e060@nordicsemi.no>

GiulianoFranchetto/zephyr,punitvara/zephyr,ldts/zephyr,explora26/zephyr,punitvara/zephyr,galak/zephyr,Vudentz/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,mbolivar/zephyr,ldts/zephyr,zephyriot/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,Vudentz/zephyr,finikorg/zephyr,ldts/zephyr,mbolivar/zephyr,explora26/zephyr,ldts/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,mbolivar/zephyr,kraj/zephyr,Vudentz/zephyr,zephyriot/zephyr,kraj/zephyr,explora26/zephyr,zephyriot/zephyr,zephyrproject-rtos/zephyr,mbolivar/zephyr,mbolivar/zephyr,finikorg/zephyr,nashif/zephyr,Vudentz/zephyr,finikorg/zephyr,finikorg/zephyr,Vudentz/zephyr,zephyriot/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,kraj/zephyr,Vudentz/zephyr,galak/zephyr,kraj/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,nashif/zephyr,finikorg/zephyr,zephyriot/zephyr,zephyrproject-rtos/zephyr,kraj/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,punitvara/zephyr,explora26/zephyr,nashif/zephyr,punitvara/zephyr,nashif/zephyr