gpg can't be enforced during pre-commit

[YodaDaCoda]

When using conform in a pre-commit hook, if using `gpg: required: true', it would seem that the previous commit is checked, not the one that's currently being committed.

Based on the git-hooks documentation I'm not sure if the current commit can be checked for signatures. IMO this should at least be documented, and ideally the behaviour adjusted.

[terlar]

This will be addressed by my PR: #262

As long as you use conform enforce --base-branch or conform enforce --revision-range.