Added runtime to readme.md
Added runtime to readme.md

Tested install.sh script to find the approximate runtime.
Test was run on a VM with 2 cores at 1800 MHz, and 4GB RAM, running in
the Alto cloud.

real    25m36.706s
user    32m46.600s
sys     6m13.231s

hioa-cs/IncludeOS,mnordsletten/IncludeOS,alfred-bratterud/IncludeOS,AndreasAakesson/IncludeOS,mnordsletten/IncludeOS,alfred-bratterud/IncludeOS,mnordsletten/IncludeOS,ingve/IncludeOS,ingve/IncludeOS,mnordsletten/IncludeOS,hioa-cs/IncludeOS,hioa-cs/IncludeOS,AndreasAakesson/IncludeOS,ingve/IncludeOS,nlitsme/IncludeOS,alfred-bratterud/IncludeOS,AndreasAakesson/IncludeOS,hioa-cs/IncludeOS,ingve/IncludeOS,hioa-cs/IncludeOS,mnordsletten/IncludeOS,AnnikaH/IncludeOS,AnnikaH/IncludeOS,nlitsme/IncludeOS,AnnikaH/IncludeOS,AndreasAakesson/IncludeOS,nlitsme/IncludeOS,AnnikaH/IncludeOS,mnordsletten/IncludeOS,alfred-bratterud/IncludeOS,ingve/IncludeOS,AndreasAakesson/IncludeOS,alfred-bratterud/IncludeOS,nlitsme/IncludeOS,AndreasAakesson/IncludeOS,AnnikaH/IncludeOS