Update README.md

Update README.md

Update README

Add Icinga 2 examples

Update README.md

Add number of stale zones in output

Fix exit code on warning

Set to python3

Improve plugin exit, add performance data

Fix error handling in MySQL connection

Fix error handling in MySQL connection

Update check_pdns_stale.py

Update README.md

Add check_dns_stale.py

Update README.md