Update Tutorial.pm

Typos
Fix typo in Git::Code::Review::Tutorial
Add the ability to date constrain the pick process.
Document the date selection in the Tutorial.
Initialization looks for the presence of tracked files in your
repository.  Git::Code::Review is designed to track your code in a
submodule.  This is a little bit of safety to prevent folks from
submoduling their code repository in their code repository.
Merge branch 'dostermeier-patch-1'