Apply Salt20 promo code to Salt guides

[nmelehan]

Applying the $20 'Salt20' promo code to all Salt guides. 16 Salt guides were found and modified:

docs git:(develop) find docs | grep index.md | egrep -i salt
docs/applications/media-servers/install-plex-media-server-with-salt/index.md
docs/applications/configuration-management/introduction-to-jinja-templates-for-salt/index.md
docs/applications/configuration-management/test-salt-locally-with-kitchen-salt/index.md
docs/applications/configuration-management/monitoring-salt-minions-with-beacons/index.md
docs/applications/configuration-management/configure-apache-with-salt-stack/index.md
docs/applications/configuration-management/automate-a-static-site-deployment-with-salt/index.md
docs/applications/configuration-management/configure-and-use-salt-ssh/index.md
docs/applications/configuration-management/use-salt-states-to-configure-a-lamp-stack-on-a-minion/index.md
docs/applications/configuration-management/use-salt-states-to-create-lamp-stack-and-fail2ban-across-salt-minions/index.md
docs/applications/configuration-management/configure-and-use-salt-cloud-and-cloud-maps-to-provision-systems/index.md
docs/applications/configuration-management/use-and-modify-official-saltstack-formulas/index.md
docs/applications/configuration-management/beginners-guide-to-salt/index.md
docs/applications/configuration-management/secrets-management-with-salt/index.md
docs/applications/configuration-management/salt-command-line-reference/index.md
docs/applications/configuration-management/create-a-salt-execution-module/index.md
docs/applications/configuration-management/getting-started-with-salt-basic-installation-and-setup/index.md

[nmelehan]

Apply Salt promo code to Salt Guides. (1)