Needs build instructions

[Gadgetoid]

Title says it all. Document git submodule installation and build/install process for the library.

Note: It's unnecessary to install/use SWIG since the bindings should be regenerated any time the git submodule is updated.

[davidbradway]

@Gadgetoid, if I install via pip (pip install rpi_ws281x), do I need to build the submodule with scons?

[Gadgetoid]

@davidbradway nope, you don't need to build anything, or even touch this repository. "pip install" should grab the appropriate .whl file for your Python version - currently I'm shipping 2.7, 3.4 and 3.5 - and that contains everything you need pre-compiled and ready to go.

Build instructions are basically just for developers.

[charliesneath]

Since it’s necessary to use sudo to use the library, is it also necessary to use sudo pip install rpi_ws281x when installing?