Implement C4
Implement C4

As discussed on <https://tree.taiga.io/project/robbt-libreairwaves-airtime-fork/issue/23>...

I am implementing the C4 standard by linking to the document in our main README.md.

LibreTime/libretime,Lapotor/libretime,LibreTime/libretime,comiconomenclaturist/libretime,Lapotor/libretime,Lapotor/libretime,comiconomenclaturist/libretime,LibreTime/libretime,Lapotor/libretime,comiconomenclaturist/libretime,comiconomenclaturist/libretime,comiconomenclaturist/libretime,comiconomenclaturist/libretime,Lapotor/libretime,LibreTime/libretime,LibreTime/libretime,comiconomenclaturist/libretime,Lapotor/libretime,LibreTime/libretime