Getting started: Make the list of packages copy-and-pastable

to a `yum install` or `apt-get install` command line.
Getting started: Correct the opencv packages required for building on Ubuntu

It's `libopencv-dev` not `libcv-dev` (the latter doesn't install the
package config file). And `libopencv-dev` automatically installs
`libhighgui-dev`.