Updated PowerDNS documentation

[rafi0101]

Hi,

I tried your documentation for PowerDNS. Unfortunately, it no longer worked as intended, so I updated it a litte bit :grinning:

Maybe you will find some typos, because I'm not always the best in spelling. Feel free to fix them :blush:

If you want, I have also an updated version for the PowerDNS-Admin documentation. But I'll need a bit of time.