Danger check for changes to package.yml files

[alexevanczuk]

Gusto has an internal danger plugin to leave an inline comment on new or modified package.yml files letting people know about some custom commands we have for working with packs, and other things to consider when manipulating package.yml files. We also use this to power a Github-based notification system for changes to alert owners when their package.yml files change.

If there is interest, we could port this over to danger-packwerk.

[schoblaska]

This seems like potentially a good idea! Leaving this issue open for now to track, though it is probably low priority for us.