Add instructions to the readme to assist new developers with contributing to the project

[djmattyg007]

In the last few weeks I've struggled a fair bit trying to work out how to do basic things such as compile the documentation, because it was all assumed knowledge. I would like to propose adding a section to the readme that details a few basic things:

• How to compile the documentation

  python setup.py build
cd docs
make html

• How to run the tests (I had to dig through a few of the various files in the tests directory before finding this one out)

  python setup.py test

I think there is one more that I can't remember right now. It wouldn't surprise me if other people have suggestions as to what should go into this, and how it should be presented.

I would also like to propose moving the changelog out of the readme file and into a separate changelog file, so as to reduce the size of the readme file, making it easier to look at.

I'd appreciate some feedback before I go ahead and create a pull request with these changes.