various small docs improvements, typos, fixes...

The last commit is adding a Makefile, and adding a few notes to the docs listing a few targets.

In my opinion (and others' too: http://www.jeffknupp.com/blog/2013/11/15/supercharge-your-python-developers/) it's a good idea to have a Makefile around with the most used commands, for a few reasons:
* ease of use, handy shortcuts
* local "documentation": what's the usual way of running tests? Let's check the Makefile (or the docs, but then, information might be spread around a few pages)
* when starting with a new project, even if you didn't read the documentation yet, you can still do the main tasks (run tests, update, reindex...)

I even go a step further on my own libs by adding a target that creates the virtualenv (locally). Eg: https://github.com/magopian/django-data-exports/blob/master/Makefile#L3

I'd love to add more targets to this file as I discover more menial and repetitive tasks/commands, please let me know if you think of any!