Suggested change to more descriptive error messages explaining how to fi...

I changed the error message on the Name and Email mismatch errors to add additional line of text describing how to correct the error, specifically what git command to type.  I've run into use cases where this could be useful especially for folks transitioning over from CVS who don't want to read any directions.  I leave it up to you as to whether you think this would be a useful change.

Thanks!