Add info on documentation to CONTRIBUTING.rst

[plammens]

I didn't find this information elsewhere in the repository; I thought it might be useful for new contributors.

[Bibo-Joshi]

Yes, this would surely be helpful :)
One suggestion:

[Poolitzer]

this does not cover windows.

On there, you need to run sphinx-build docs\source temp_html or so :)

[plammens]

this does not cover windows.

On there, you need to run sphinx-build docs\source temp_html or so :)

Right, forgot about that. I'm using Windows, and I have installed make through cygwin, but probably its best to add the alternative in any case! I've re-amended the commit.

[Poolitzer]

uhm, there exists requirements-docs.txt in the docs folder, which people need to install with pip -r. Sorry that I only think of that now ;P

[plammens]

uhm, there exists requirements-docs.txt in the docs folder, which people need to install with pip -r. Sorry that I only think of that now ;P

Ha! I also missed that. I've added it now.

[Eldinnie]

Hi,
Thanks again for contributing!