contribs: Fix whitespace issue

Inside help description one "space" was in fact a tab. It should not hurt
final user but will be a problem while preparing tests that analyze output
of this script.
contribs: Use 'printf' instead of 'echo'

Such change will increase portability because any new lines will be added
only explicitly.
Fix issue running script on Windows

To make the script work on Windows keeping Git Bash as the only one
dependency, paste command will be emulated. It is implemented in a very simple
way and its efficiency is VERY bad. Additional step-by-step instruction how to
overcome this issue is now added to README file.