Request: improve information around "Unable to restore working tree after pre-commit hooks run" #504

When the user is notified that Overcommit is

Unable to restore working tree after pre-commit hooks run

it would be helpful to explain that their working tree has been stashed.

There are presumably very good reasons for Overcommit to stash the working tree. But I cannot think of any reason not to inform the user of this, or to assume they already are aware of it.

I expect this would help resolve problems like #135 .