Add nsjail upstream url

Add nsjail upstream url

Please keep the latest upstream source code in the upstream-git by using the url in "#X-Vcs-Url"

You can update the upstream manually. Following commands can be used to keep the latest upstream source code.
 $ git remote add upstream https://github.com/google/nsjail.git
 $ git fetch --all
 $ git checkout upstream-git
 $ git rebase upstream/master
 $ git push origin upstream-git:upstream-git