The `setup` script is there for quite a while but is still
not described in the README.md, so the documentation teaches
the users how to set up the environment the hard way.

This commit makes it easier for the newcomers to set up
the build environment.

Change-Id: I1901273246567ff2c211edb251f65106263daf6f
Signed-off-by: Alexander Amelkin <a.amelkin@yadro.com>