Add section about Salsa for new maintainers
Explain the importance of Salsa (Debian's GitLab instance) to new maintainers. Add a new section in newmaint.wml that describes what Salsa is, its benefits, and basic steps to get started. This helps newcomers understand a crucial part of Debian's development infrastructure early in their journey.
Also clean away some trailing whitespace.
Edited by Otto Kekäläinen