git log failed

When using `php composer.phar create-project cyberspectrum/contao-toolbox` composer will use archive mode by default. In this case, the compile fail, because the git informations are missing in https://github.com/cyberspectrum/contao-toolbox/blob/master/src/CyberSpectrum/Compiler.php#L27

The correct call is `php composer.phar create-project --prefer-source cyberspectrum/contao-toolbox`.
Add a hint for the "remove vcs history" question.
Merge pull request #13 from tristanlins/patch-1

Clearify documentation to circumvent error `git log failed when compiling.`