Zeal docset for D

[Dejan Lekic]

Thanks to Matheus França who posted this on Discord today:

http://zealusercontributions.vercel.app/api/docsets/D.xml

It contains Zeal (https://zealdocs.org) docset with D 
documentation. Whoever did this - thank you! - I wanted to do it 
myself and could never find time to do it...

![Here is Zeal with D docset in 
action](https://gcdnb.pbrd.co/images/Ne4fz2cAm55c.png?o=1).