Update tutorial documentation to work with Ubuntu 12.04

There could be a better solution here then just building as a binary package, but here are the two problems I just ran into when installing this on Ubuntu 12.04:

##### equiv not installed

Easy enough, I saw there was another pull request that had this + some other stuff in it as well after the fact, but included it in here anyway.

    $ sudo mk-build-deps -ri
    mk-build-deps: You must have equivs installed to use this program.

##### no upstream tarball found

    $ dpkg-buildpackage -us -uc
    dpkg-buildpackage: source package dh-virtualenv
    dpkg-buildpackage: source version 0.6-1
    dpkg-buildpackage: source changed by Jyrki Pulliainen <jyrki@spotify.com>
    dpkg-buildpackage: host architecture amd64
     dpkg-source --before-build dh-virtualenv
     fakeroot debian/rules clean

    -- snip --

    dh clean --with python2 --with sphinxdoc
       dh_testdir
       dh_auto_clean
    running clean
    'build/lib.linux-x86_64-2.7' does not exist -- can't clean it
    'build/bdist.linux-x86_64' does not exist -- can't clean it
    'build/scripts-2.7' does not exist -- can't clean it
       dh_clean
     dpkg-source -b dh-virtualenv
    dpkg-source: error: can't build with source format '3.0 (quilt)': no upstream tarball found at ../dh-virtualenv_0.6.orig.tar.{bz2,gz,lzma,xz}
    dpkg-buildpackage: error: dpkg-source -b dh-virtualenv gave error exit status 255
    debuild: fatal error at line 1350:
    dpkg-buildpackage -rfakeroot -D -us -uc failed

Let me know if there is a better solution, or just something that I have missed :)