Adjustment of the 'Advanced usage' in the README

[chrboesch]

The 'advanced usage' still needs to be adjusted, both in the build system and in the readme.

[perillo]

It is already working in the build system; only the README.md file needs to be updated.

Unfortunately, I missed the Advanced Usage section in commit 0d56ba3; sorry for the inconvenience.

[chrboesch]

see #212 (comment)