Add item to TODO list
Implement 'fetch' sub-command and reimplement 'checkout' upon it

The 'git gerrit fetch' sub-command fetches a list of changes and
creates local change-branches. The 'checkout' does that (invoking
fetch first) and then checks out the last change-branch.
Make 'cherry-pick' accept a list of CHANGES

Now 'cherry-pick' invokes 'fetch' to fetch the changes from Gerrit,
just like 'checkout'. This is very much useful to do work on top of a
bunch of changes still pending revision.
Document workflow using 'cherry-pick' sub-command