Merge in DNS/adguard-home from 2294-changelog to master
Closes#2294.
Squashed commit of the following:
commit 25ffc9786d23d83448b916a81f0b20135b051169
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date: Thu Nov 12 19:40:48 2020 +0300
all: add a changelog and a developer guide