It looks like that branch supports 5.6 and the readme should get you pretty far but in case thats not enough I did do a video of building from source. https://www.youtube.com/watch?v=Bp6fR-hCVoE
Now this was on OSX but the major steps would be the same - Install deps from github readme - Build and install the extension - Make sure the extension is in your php.ini file that apache is looking for - Party