This is implemented by defining ${DOMAINS_TXT} in config.sh. If not
set in config.sh, it defaults to the previously (hard-coded) location,
which is ${BASEDIR}/domains.txt.

Update wellknown.md

apache config that would work for 1.3, 2.0, 2.2 and 2.4

This reverts commit 4dc99533.

I have no idea why I thought reusing the keys would be a good idea
when I first started this...

wellknown.md: Clarify WELLKNOWN variable