Migration of users from SVN to Git may fail

There's following paragraph in the book:

> To get a list of the author names that SVN uses, you can run this:
```
$ svn log --xml | grep -P "^<author" | sort -u | \
      perl -pe 's/<author>(.*?)<\/author>/$1 = /' > users.txt
```

But in fact, if user checked out **just `trunk`** or some other specific path from the whole repo, `svn log` will by default look for revisions **only for that particular path**.
We can make sure all users will get all revisions within the whole repo just by adding root as an explicit PATH.