docs: Add more prerequisites
docs: Add more prerequisites

On Ubuntu 16.04.1, there are a few more packages needed to be able to
run `make menuconfig` on Linux kernel.

Signed-off-by: Joakim Bech <741f90e2a7f4d9afbad8bd50be20560f4cf38962@linaro.org>
Reviewed-by: Jens Wiklander <7706914404370d7502c27a0eff493dcf491feb51@linaro.org>
Reviewed-by: David Brown <0af22db655f3ade5845314d695c1f4910314b0cb@linaro.org>

pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,matt2048/optee_os,pascal-brand-st-dev/optee_os,matt2048/optee_os,matt2048/optee_os,pascal-brand-st-dev/optee_os,matt2048/optee_os