Better pycairo installation instructions in docs

I just wanted to point out that pycairo can be found in [this GitHub repo](https://github.com/pygobject/pycairo), and that there it says installing it is as simple as `pip install pycairo`. Am I missing something or should this information be included in the docs? It would be much easier than locating and installing the appropriate version from [here](https://www.lfd.uci.edu/~gohlke/pythonlibs/#pycairo) as the docs say.

** Also, this is my first issue, so please tell me if I'm doing something wrong.