doc:it: add some process/* translations

Translated documents:
- 2.Process
- 3.Early-stage
- 4.Coding
- 5.Posting
- 6.Followthrough
- 7.AdvancedTopics
- 8.Conclusion
- adding-syscalls

Signed-off-by: Federico Vaga <federico.vaga@vaga.pv.it>
Signed-off-by: Alessia Mantegazza <amantegazza@vaga.pv.it>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>