docs: tracing.md: add a "how to get traces" chapter
docs: tracing.md: add a "how to get traces" chapter

This chapter describes how to get tracing information.

Signed-off-by: Vlad Zolotarov <976c0f8d0852ed6439ad273880b400a75a7c41d0@scylladb.com>

avikivity/scylla,avikivity/scylla,scylladb/scylla,duarten/scylla,duarten/scylla,duarten/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla