Changed the psycopg2 install method for Windows.

[bmispelon]

The current suggested method relies on git being installed
on the user's machine.
This new one is slightly more complex (there's an
extra step of downloading a prebuilt binary) but
it should work with nothing else installed.

[maciejgryka]

Another option would be to ask to install Heroku Toolbelt (which includes git) at this point instead of later on. Maybe that would be easier?

[bmispelon]

True, I hadn't thought about that.

Frankly, I'm too tired to think right now but I wanted to open the PR before going to bed. Hopefully I'll be smarter in the morning and we can find a way that works.

Thanks.

[maciejgryka]

Oh crap, I'm sorry, I accidentally pushed an alternative solution to this repo instead of my private one. Happy to take it back if people prefer this option.

[olasitarska]

I think the solution proposed by @maciejgryka is easier. @bmispelon, can you confirm that it would work?

[maciejgryka]

FYI - we've just finished a setup session, and the way I suggested didn't work (not sure why, I'll try to investigate tomorrow). In the end @bmispelon's solution did the trick though!

[olasitarska]

@maciejgryka ok, so I'm going to resolve conflict and merge @bmispelon solution. Thanks guys!