Turn off htmlproofer and see if it's possible to run as a monthly cron job

[uditvira]

it's way too noisy for the amount of time we have

[uditvira]

@ASoTNetworks is investigating possibility to fail more gracefully

[ASoTNetworks]

I have created a PR #58 that adds disable_external to HTMLProofer that disables external link checks so it should create less noise. I have also updated the readme about links are not being checked.