Add explanation of how to build #4
Description
Right now, anyone who wants to build this library has to set up the environment variable CC on their computer (do to limitations with leanc)
I was able to get it to build on Windows by using https://github.com/skeeto/w64devkit and then setting CC using
$Env:CC = "C:\github\w64devkit\w64devkit\bin\gcc.exe"
on powershell