Clarifies where `--source-map-inline-sources` output goes.
Clarifies where `--source-map-inline-sources` output goes.

See https://github.com/jakubpawlowicz/clean-css/issues/397#issuecomment-90896687
yomed/clean-css,island205/clean-css,shelsonjava/clean-css,jakubpawlowicz/clean-css,scottgonzalez/clean-css,GerHobbelt/clean-css,MartyIX/clean-css,vlajos/clean-css,stuht/clean-css