v1.6.8: Fix network creation conflict for new installs

What changed

• Fix network creation conflict (#10): The manual docker network create step in SETUP.md conflicted with the network definition in docker-compose.traefik.yml, causing Compose to fail with "Pool overlaps with other one on this address space". All compose files now define the network consistently with name: arr-stack, and Compose creates it automatically. The manual step has been removed from SETUP.md. Thanks @eren-kemer!
• Docs fix: Corrected inaccurate note in UPGRADING.md that claimed TROUBLESHOOTING.md was removed (it still exists).

New installs

No action needed — just follow the updated SETUP.md.

Existing installs

cd /volume1/docker/arr-stack
git pull

# Stop everything, remove old manually-created network, restart
docker compose -f docker-compose.arr-stack.yml -f docker-compose.traefik.yml -f docker-compose.utilities.yml down
docker compose -f docker-compose.cloudflared.yml down 2>/dev/null
docker network rm arr-stack
docker compose -f docker-compose.arr-stack.yml -f docker-compose.traefik.yml -f docker-compose.utilities.yml up -d
docker compose -f docker-compose.cloudflared.yml up -d 2>/dev/null

Note: If other containers use the arr-stack network, disconnect them before removing the network, then recreate them after to pick up the new network ID.