systemd: update README

Discourage use of kresd.service in distros using systemd-sysv-generator.
15 jobs for <span class="ref-name">systemd-revision</span> in 9 minutes and 33 seconds (queued for 7 seconds)
Status Job ID Name Coverage
  Build
passed #110321
docker linux amd64
build:clang:linux:amd64

00:00:34

passed #110320
docker linux amd64
build:linux:amd64

00:00:39

 
  Test
passed #110328
docker linux amd64
deckard:linux:amd64

00:08:10

passed #110327
docker
doc

00:01:13

passed #110326
docker linux amd64
installcheck:linux:amd64

00:01:35

passed #110329
docker linux amd64
installcheck:valgrind:linux:amd64

00:02:05

passed #110323
docker
lint:c

00:02:56

failed #110324
docker allowed to fail
lint:clang-scan-build

00:01:44

passed #110322
docker
lint:lua

00:00:46

passed #110332
docker linux amd64
respdiff:iter:tcp:linux:amd64

00:02:27

passed #110333
docker linux amd64
respdiff:iter:tls:linux:amd64

00:02:26

passed #110331
docker linux amd64
respdiff:iter:udp:linux:amd64

00:03:22

passed #110325
docker linux amd64
test:linux:amd64

00:01:21

passed #110330
docker linux amd64
test:linux:amd64:valgrind

00:01:24

 
  Coverage
passed #110334
docker linux amd64
coverage

00:00:42

70.1%
 
Name Stage Failure
failed
lint:clang-scan-build Test
  CCLD	modules/hints/hints.so
CCLD modules/stats/stats.so
CCLD modules/cookies/cookies.so
scan-build: 22 bugs found.
scan-build: Run 'scan-view /builds/knot/knot-resolver/scan-results/2018-02-16-113501-13-1' to examine bug reports.
Uploading artifacts...
scan-results: found 27 matching files
Uploading artifacts to coordinator... ok id=110324 responseStatus=201 Created token=TAkPfkx3
ERROR: Job failed: exit code 1