Update installation instructions to reflect wheels

[GadgetSteve]

Currently the installation instructions read:

First you need to install it, which you can do by typing:

tar xvzf netifaces-0.10.8.tar.gz
cd netifaces-0.10.8
python setup.py install
Note that you will need the relevant developer tools for your platform, as netifaces is written in C and installing this way will compile the extension.

This does not reflect that wheels are now available and may frighten off many potential users. I suggest something like:

pip install --prefer-binary netifaces will install the latest released wheel for your platform, to use the latest release or if a wheel is not available for your platform you will need the relevant developer tools for your platform as netifaces is written in C. For the latest cutting edge version, complete with any unresolved issues, you can download or check out from GitHub and build with ....

As an aside I would suggest removing the version numbers (0.10.8 above) to reduce the frequency of needing to update the docs.