Print link to commit guidelines when commit linting fails

[achingbrain]

Commit linting errors can be pretty opaque to first-time contributors.

The rules are well documented but hard to discover, so it'd be helpful if aegir would print a link to the linting rules when commit linting fails to help contributors self-diagnose what the issue is.

cc @terichadbourne

[hugomrdias]

should we instead remove commit-lint support ? we don't use it anymore