nRF52840 adaptation: Added table of contents to bring-up app README.
nRF52840 adaptation: Added table of contents to bring-up app README.

openweave/openweave-core,openweave/openweave-core,openweave/openweave-core,openweave/openweave-core,openweave/openweave-core,openweave/openweave-core