CODEOWNERS: add owners for docs/
CODEOWNERS: add owners for docs/

User documentation was recently migrated to scylla.git, and this is
maintained by non scylla-core people. Add entries for docs/ so they are
notified when somebody submits changes to docs/.

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla