Clarify quick start with manual cron setup

[bradthx]

Summary

1. Expand quick start into an end to end setup flow.
2. Add explicit manual cron install and validation steps.
3. Keep examples generic with /path/to/monitor and direct commands.

Validation

1. python3 -m py_compile ndrift tests/test_ndrift.py
2. python3 -m unittest -q tests/test_ndrift.py