Add 'Lezione 04'

src/04_open-source/00_index.md

src/04_open-source/01_letteratura/00_index.md

src/04_open-source/01_letteratura/01_cathedral-bazaar.md

src/04_open-source/01_letteratura/02_care-feeding.md

...en-source/01_letteratura/03_emerging-economic-paradigm.md

src/04_open-source/01_letteratura/04_empirical-study.md

src/04_open-source/02_sfide.md

src/SUMMARY.md