Document the need to have libncurses5 installed
Document the need to have libncurses5 installed

The prebuilt version of clang requires `libtinfo.so.5` to be present,
which is provided by ncurses5.

Signed-off-by: Philipp Wagner <5a4b10454c30419e54a1570be358a516ff84bb63@lowrisc.org>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan