Update philosophy.rst
Update tutorial-2.rst
Update tutorial-3.rst
Merge pull request #15 from jmsbrry/master

Cleanup of typos and formatting errors in docs.
Make example in README copy & paste-able.

The example in 'Problems using virtualenv under
Ubuntu' is made copy&paste-able by using the
$VIRTUAL_ENV variable instead of the placeholder
<your virtualenv dir>.
Merge pull request #18 from gregmuellegger/copyable-venv-fix

Make example in README copy & paste-able.